diff --git a/Libraries/SPTarkov.Server.Core/Controllers/BuildController.cs b/Libraries/SPTarkov.Server.Core/Controllers/BuildController.cs
index af9717ef..688b595f 100644
--- a/Libraries/SPTarkov.Server.Core/Controllers/BuildController.cs
+++ b/Libraries/SPTarkov.Server.Core/Controllers/BuildController.cs
@@ -87,29 +87,29 @@ public class BuildController(
     ///     Handle client/builds/weapon/save
     /// </summary>
     /// <param name="sessionId">Session/Player id</param>
-    /// <param name="body"></param>
-    public void SaveWeaponBuild(MongoId sessionId, PresetBuildActionRequestData body)
+    /// <param name="request"></param>
+    public void SaveWeaponBuild(MongoId sessionId, PresetBuildActionRequestData request)
     {
         var pmcData = profileHelper.GetPmcProfile(sessionId);
 
         // Replace duplicate Id's. The first item is the base item.
         // The root ID and the base item ID need to match.
-        body.Items = itemHelper.ReplaceIDs(body.Items, pmcData);
-        body.Root = body.Items.FirstOrDefault().Id;
+        request.Items = itemHelper.ReplaceIDs(request.Items, pmcData);
+        request.Root = request.Items.FirstOrDefault().Id;
 
         // Create new object ready to save into profile userbuilds.weaponBuilds
         var newBuild = new WeaponBuild
         {
-            Id = body.Id,
-            Name = body.Name,
-            Root = body.Root,
-            Items = body.Items,
+            Id = request.Id,
+            Name = request.Name,
+            Root = request.Root,
+            Items = request.Items.ToList(),
         };
 
         var profile = profileHelper.GetFullProfile(sessionId);
 
         var savedWeaponBuilds = profile.UserBuildData.WeaponBuilds;
-        var existingBuild = savedWeaponBuilds.FirstOrDefault(x => x.Id == body.Id);
+        var existingBuild = savedWeaponBuilds.FirstOrDefault(x => x.Id == request.Id);
         if (existingBuild is not null)
         {
             // exists, replace
@@ -146,8 +146,8 @@ public class BuildController(
             Id = request.Id,
             Name = request.Name,
             BuildType = EquipmentBuildType.Custom,
-            Root = request.Items[0].Id,
-            Items = request.Items,
+            Root = request.Items.First().Id,
+            Items = request.Items.ToList(),
         };
 
         var existingBuild = existingSavedEquipmentBuilds?.FirstOrDefault(build =>
diff --git a/Libraries/SPTarkov.Server.Core/Controllers/InsuranceController.cs b/Libraries/SPTarkov.Server.Core/Controllers/InsuranceController.cs
index ac88d71b..cffc2b7d 100644
--- a/Libraries/SPTarkov.Server.Core/Controllers/InsuranceController.cs
+++ b/Libraries/SPTarkov.Server.Core/Controllers/InsuranceController.cs
@@ -66,7 +66,7 @@ public class InsuranceController(
         var insuranceDetails = FilterInsuredItems(sessionId);
 
         // Skip profile if no insured items to process
-        if (insuranceDetails.Count == 0)
+        if (!insuranceDetails.Any())
         {
             return;
         }
@@ -80,7 +80,7 @@ public class InsuranceController(
     /// <param name="sessionId">Session/Player id</param>
     /// <param name="time">The time to check ready status against. Current time by default</param>
     /// <returns>All insured items that are ready to be processed</returns>
-    protected List<Insurance> FilterInsuredItems(MongoId sessionId, long? time = null)
+    protected IEnumerable<Insurance> FilterInsuredItems(MongoId sessionId, long? time = null)
     {
         // Use the current time by default.
         var insuranceTime = time ?? timeUtil.GetTimeStamp();
@@ -96,9 +96,7 @@ public class InsuranceController(
             }
         }
 
-        return profileInsuranceDetails
-            .Where(insured => insuranceTime >= insured.ScheduledTime)
-            .ToList();
+        return profileInsuranceDetails.Where(insured => insuranceTime >= insured.ScheduledTime);
     }
 
     /// <summary>
@@ -106,12 +104,12 @@ public class InsuranceController(
     /// </summary>
     /// <param name="insuranceDetails">The insured items to process</param>
     /// <param name="sessionId">session ID that should receive the processed items</param>
-    protected void ProcessInsuredItems(List<Insurance> insuranceDetails, MongoId sessionId)
+    protected void ProcessInsuredItems(IEnumerable<Insurance> insuranceDetails, MongoId sessionId)
     {
         if (logger.IsLogEnabled(LogLevel.Debug))
         {
             logger.Debug(
-                $"Processing {insuranceDetails.Count} insurance packages, which includes a total of: {CountAllInsuranceItems(insuranceDetails)} items, in profile: {sessionId}"
+                $"Processing {insuranceDetails.Count()} insurance packages, which includes a total of: {CountAllInsuranceItems(insuranceDetails)} items, in profile: {sessionId}"
             );
         }
 
@@ -149,7 +147,7 @@ public class InsuranceController(
     /// </summary>
     /// <param name="insuranceDetails"></param>
     /// <returns>Count of insured items</returns>
-    protected int CountAllInsuranceItems(List<Insurance> insuranceDetails)
+    protected int CountAllInsuranceItems(IEnumerable<Insurance> insuranceDetails)
     {
         return insuranceDetails.Select(ins => ins.Items.Count).Count();
     }
@@ -238,13 +236,13 @@ public class InsuranceController(
     /// <param name="insured">The insurance object containing the items to evaluate</param>
     /// <param name="itemsMap">A Dictionary for quick item look-up by item ID</param>
     /// <returns>A dictionary containing parent item IDs to arrays of their attachment items</returns>
-    protected Dictionary<string, List<Item>> PopulateParentAttachmentsMap(
+    protected Dictionary<MongoId, List<Item>> PopulateParentAttachmentsMap(
         string rootItemParentID,
         Insurance insured,
         Dictionary<MongoId, Item> itemsMap
     )
     {
-        var mainParentToAttachmentsMap = new Dictionary<string, List<Item>>();
+        var mainParentToAttachmentsMap = new Dictionary<MongoId, List<Item>>();
         foreach (var insuredItem in insured.Items)
         {
             // Use the parent ID from the item to get the parent item.
@@ -335,12 +333,12 @@ public class InsuranceController(
     /// <param name="parentAttachmentsMap">Dictionary containing parent item IDs to arrays of their attachment items</param>
     /// <param name="itemsMap">Hashset containing parent item IDs to arrays of their attachment items which are not moddable in-raid</param>
     /// <returns></returns>
-    protected Dictionary<string, List<Item>> RemoveNonModdableAttachments(
-        Dictionary<string, List<Item>> parentAttachmentsMap,
+    protected Dictionary<MongoId, List<Item>> RemoveNonModdableAttachments(
+        Dictionary<MongoId, List<Item>> parentAttachmentsMap,
         Dictionary<MongoId, Item> itemsMap
     )
     {
-        var updatedMap = new Dictionary<string, List<Item>>();
+        var updatedMap = new Dictionary<MongoId, List<Item>>();
 
         foreach (var map in parentAttachmentsMap)
         {
@@ -389,7 +387,7 @@ public class InsuranceController(
     protected void ProcessRegularItems(
         Insurance insured,
         HashSet<MongoId> toDelete,
-        Dictionary<string, List<Item>> parentAttachmentsMap
+        Dictionary<MongoId, List<Item>> parentAttachmentsMap
     )
     {
         foreach (var insuredItem in insured.Items)
@@ -436,7 +434,7 @@ public class InsuranceController(
     /// <param name="insuredTraderId">Trader ID from the Insurance object</param>
     /// <param name="toDelete">Tracked attachment ids to be removed</param>
     protected void ProcessAttachments(
-        Dictionary<string, List<Item>> mainParentToAttachmentsMap,
+        Dictionary<MongoId, List<Item>> mainParentToAttachmentsMap,
         Dictionary<MongoId, Item> itemsMap,
         MongoId? insuredTraderId,
         HashSet<MongoId> toDelete
@@ -474,7 +472,7 @@ public class InsuranceController(
     /// <param name="traderId">ID of the trader to that has ensured these items</param>
     /// <param name="toDelete">array that accumulates the IDs of the items to be deleted</param>
     protected void ProcessAttachmentByParent(
-        List<Item> attachments,
+        IEnumerable<Item> attachments,
         MongoId traderId,
         HashSet<MongoId> toDelete
     )
@@ -522,8 +520,8 @@ public class InsuranceController(
     /// <param name="attachments"></param>
     /// <param name="attachmentPrices"></param>
     protected void LogAttachmentsBeingRemoved(
-        List<MongoId> attachmentIdsToRemove,
-        List<Item> attachments,
+        IEnumerable<MongoId> attachmentIdsToRemove,
+        IEnumerable<Item> attachments,
         Dictionary<MongoId, double> attachmentPrices
     )
     {
@@ -547,7 +545,7 @@ public class InsuranceController(
     /// </summary>
     /// <param name="attachments">Item attachments</param>
     /// <returns></returns>
-    protected Dictionary<MongoId, double> WeightAttachmentsByPrice(List<Item> attachments)
+    protected Dictionary<MongoId, double> WeightAttachmentsByPrice(IEnumerable<Item> attachments)
     {
         var result = new Dictionary<MongoId, double>();
 
diff --git a/Libraries/SPTarkov.Server.Core/Controllers/InventoryController.cs b/Libraries/SPTarkov.Server.Core/Controllers/InventoryController.cs
index 5c49fb01..d4aa2524 100644
--- a/Libraries/SPTarkov.Server.Core/Controllers/InventoryController.cs
+++ b/Libraries/SPTarkov.Server.Core/Controllers/InventoryController.cs
@@ -183,7 +183,7 @@ public class InventoryController(
     {
         // The client sends the full list of favorite items, so clear the current favorites
         pmcData.Inventory.FavoriteItems = [];
-        pmcData.Inventory.FavoriteItems.AddRange(request.Items);
+        pmcData.Inventory.FavoriteItems = pmcData.Inventory.FavoriteItems.Union(request.Items);
     }
 
     /// <summary>
diff --git a/Libraries/SPTarkov.Server.Core/Controllers/TradeController.cs b/Libraries/SPTarkov.Server.Core/Controllers/TradeController.cs
index a8ca63cb..80885fd1 100644
--- a/Libraries/SPTarkov.Server.Core/Controllers/TradeController.cs
+++ b/Libraries/SPTarkov.Server.Core/Controllers/TradeController.cs
@@ -336,7 +336,7 @@ public class TradeController(
     /// <returns>Rouble price</returns>
     protected int GetPriceOfItemAndChildren(
         MongoId parentItemId,
-        List<Item> items,
+        IEnumerable<Item> items,
         Dictionary<MongoId, int?> handbookPrices,
         TraderBase traderDetails
     )
diff --git a/Libraries/SPTarkov.Server.Core/Generators/BotEquipmentModGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/BotEquipmentModGenerator.cs
index c9ad3f27..d591dbfb 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/BotEquipmentModGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/BotEquipmentModGenerator.cs
@@ -197,7 +197,8 @@ public class BotEquipmentModGenerator(
                 );
                 switch (plateSlotFilteringOutcome.Result)
                 {
-                    case Result.UNKNOWN_FAILURE or Result.NO_DEFAULT_FILTER:
+                    case Result.UNKNOWN_FAILURE
+                    or Result.NO_DEFAULT_FILTER:
                         if (logger.IsLogEnabled(LogLevel.Debug))
                         {
                             logger.Debug(
@@ -1125,7 +1126,7 @@ public class BotEquipmentModGenerator(
         var parentSlot = request.ParentTemplate.Properties.Slots?.FirstOrDefault(i =>
             i.Name == request.ModSlot
         );
-        var weaponTemplate = itemHelper.GetItem(request.Weapon[0].Template).Value;
+        var weaponTemplate = itemHelper.GetItem(request.Weapon.First().Template).Value;
 
         // It's ammo, use predefined ammo parameter
         if (GetAmmoContainers().Contains(request.ModSlot) && request.ModSlot != "mod_magazine")
@@ -1155,7 +1156,7 @@ public class BotEquipmentModGenerator(
             if (modPool.Count > 1)
             {
                 modPool = FilterSightsByWeaponType(
-                    request.Weapon[0],
+                    request.Weapon.First(),
                     modPool,
                     request.BotWeaponSightWhitelist
                 );
@@ -1261,7 +1262,7 @@ public class BotEquipmentModGenerator(
             if (parentSlot.Required.GetValueOrDefault(false))
             {
                 logger.Warning(
-                    $"Required slot unable to be filled, {request.ModSlot} on {request.ParentTemplate.Name} {request.ParentTemplate.Id} for weapon: {request.Weapon[0].Template}"
+                    $"Required slot unable to be filled, {request.ModSlot} on {request.ParentTemplate.Name} {request.ParentTemplate.Id} for weapon: {request.Weapon.First().Template}"
                 );
             }
 
@@ -1323,7 +1324,7 @@ public class BotEquipmentModGenerator(
         HashSet<MongoId> modPool,
         Slot parentSlot,
         ModSpawn? choiceTypeEnum,
-        List<Item> weapon,
+        IEnumerable<Item> weapon,
         string modSlotName
     )
     {
@@ -1366,7 +1367,7 @@ public class BotEquipmentModGenerator(
     public ChooseRandomCompatibleModResult GetCompatibleModFromPool(
         HashSet<MongoId> modPool,
         ModSpawn? modSpawnType,
-        List<Item> weapon
+        IEnumerable<Item> weapon
     )
     {
         // Create exhaustable pool to pick mod item from
@@ -1649,11 +1650,11 @@ public class BotEquipmentModGenerator(
     /// <param name="weapon">Array of items that make up a weapon</param>
     /// <param name="modTpl">Mod to check compatibility with weapon</param>
     /// <returns>True if incompatible</returns>
-    public bool WeaponModComboIsIncompatible(List<Item> weapon, MongoId modTpl)
+    public bool WeaponModComboIsIncompatible(IEnumerable<Item> weapon, MongoId modTpl)
     {
         // STM-9 + AR-15 Lone Star Ion Lite handguard
         if (
-            weapon[0].Template == ItemTpl.SMG_SOYUZTM_STM9_GEN2_9X19_CARBINE
+            weapon.First().Template == ItemTpl.SMG_SOYUZTM_STM9_GEN2_9X19_CARBINE
             && modTpl == ItemTpl.HANDGUARD_AR15_LONE_STAR_ION_LITE
         )
         {
@@ -1714,7 +1715,7 @@ public class BotEquipmentModGenerator(
         MongoId fallbackModTpl,
         Slot parentSlot,
         string modSlot,
-        List<Item> items
+        IEnumerable<Item> items
     )
     {
         // Find compatible mods and make an array of them
diff --git a/Libraries/SPTarkov.Server.Core/Generators/BotLootGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/BotLootGenerator.cs
index df64341f..cda42851 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/BotLootGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/BotLootGenerator.cs
@@ -552,7 +552,7 @@ public class BotLootGenerator(
                 new()
                 {
                     Id = newRootItemId,
-                    Template = itemToAddTemplate?.Id ?? string.Empty,
+                    Template = itemToAddTemplate?.Id ?? MongoId.Empty(),
                     Upd = botGeneratorHelper.GenerateExtraPropertiesForItem(
                         itemToAddTemplate,
                         botRole
diff --git a/Libraries/SPTarkov.Server.Core/Generators/BotWeaponGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/BotWeaponGenerator.cs
index 11b07388..784b748a 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/BotWeaponGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/BotWeaponGenerator.cs
@@ -619,7 +619,7 @@ public class BotWeaponGenerator(
     /// <param name="botRole">The bot type we are getting the magazine for.</param>
     /// <returns>Magazine template string.</returns>
     protected MongoId? GetMagazineTemplateFromWeaponTemplate(
-        List<Item> weaponMods,
+        IEnumerable<Item> weaponMods,
         TemplateItem weaponTemplate,
         string botRole
     )
diff --git a/Libraries/SPTarkov.Server.Core/Generators/FenceBaseAssortGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/FenceBaseAssortGenerator.cs
index ffc699df..802c274d 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/FenceBaseAssortGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/FenceBaseAssortGenerator.cs
@@ -35,7 +35,7 @@ public class FenceBaseAssortGenerator(
     public void GenerateFenceBaseAssorts()
     {
         var blockedSeasonalItems = seasonalEventService.GetInactiveSeasonalEventItems();
-        var baseFenceAssort = databaseService.GetTrader(Traders.FENCE).Assort;
+        var baseFenceAssort = databaseService.GetTrader(Traders.FENCE)?.Assort;
 
         foreach (var (itemId, rootItemDb) in databaseService.GetItems())
         {
@@ -165,7 +165,7 @@ public class FenceBaseAssortGenerator(
             }
 
             // Construct preset + mods
-            var itemAndChildren = _cloner.Clone(defaultPreset.Items).ReplaceIDs().ToList();
+            var itemAndChildren = _cloner.Clone(defaultPreset.Items).ReplaceIDs();
 
             // Find root item and add some properties to it
             var rootItem = itemAndChildren.FirstOrDefault(item =>
@@ -187,7 +187,7 @@ public class FenceBaseAssortGenerator(
             var itemQualityModifier = itemHelper.GetItemQualityModifierForItems(itemAndChildren);
 
             // Multiply weapon+mods rouble price by quality modifier
-            baseFenceAssort.BarterScheme[itemAndChildren[0].Id] =
+            baseFenceAssort.BarterScheme[itemAndChildren.First().Id] =
             [
                 new()
                 {
@@ -199,7 +199,7 @@ public class FenceBaseAssortGenerator(
                 },
             ];
 
-            baseFenceAssort.LoyalLevelItems[itemAndChildren[0].Id] = 1;
+            baseFenceAssort.LoyalLevelItems[itemAndChildren.First().Id] = 1;
         }
     }
 
diff --git a/Libraries/SPTarkov.Server.Core/Generators/LocationLootGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/LocationLootGenerator.cs
index 64106ba7..cb97567c 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/LocationLootGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/LocationLootGenerator.cs
@@ -624,8 +624,8 @@ public class LocationLootGenerator(
             );
 
             // Update root item properties with result of position finder
-            items[0].SlotId = "main";
-            items[0].Location = new ItemLocation
+            items.First().SlotId = "main";
+            items.First().Location = new ItemLocation
             {
                 X = result.X,
                 Y = result.Y,
@@ -1460,7 +1460,7 @@ public record ContainerGroupCount
 public class ContainerItem
 {
     [JsonPropertyName("items")]
-    public List<Item>? Items { get; set; }
+    public IEnumerable<Item>? Items { get; set; }
 
     [JsonPropertyName("width")]
     public int? Width { get; set; }
diff --git a/Libraries/SPTarkov.Server.Core/Generators/RagfairAssortGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/RagfairAssortGenerator.cs
index e1517b42..6323397f 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/RagfairAssortGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/RagfairAssortGenerator.cs
@@ -41,7 +41,7 @@ public class RagfairAssortGenerator(
     ///     Each sub list contains item + children (if any)
     /// </summary>
     /// <returns> List with children lists of items </returns>
-    public List<List<Item>> GetAssortItems()
+    public IEnumerable<List<Item>> GetAssortItems()
     {
         return GenerateRagfairAssortItems();
     }
@@ -50,9 +50,9 @@ public class RagfairAssortGenerator(
     ///     Generate a list of lists (item + children) the flea can sell
     /// </summary>
     /// <returns> List of lists (item + children)</returns>
-    protected List<List<Item>> GenerateRagfairAssortItems()
+    protected IEnumerable<List<Item>> GenerateRagfairAssortItems()
     {
-        List<List<Item>> results = [];
+        IEnumerable<List<Item>> results = [];
 
         // Get cloned items from db
         var dbItems = databaseService
@@ -76,16 +76,16 @@ public class RagfairAssortGenerator(
             // Add presets base item tpl to the processed list so its skipped later on when processing items
             processedArmorItems.Add(preset.Items[0].Template);
 
-            presetAndModsClone[0].ParentId = "hideout";
-            presetAndModsClone[0].SlotId = "hideout";
-            presetAndModsClone[0].Upd = new Upd
+            presetAndModsClone.First().ParentId = "hideout";
+            presetAndModsClone.First().SlotId = "hideout";
+            presetAndModsClone.First().Upd = new Upd
             {
                 StackObjectsCount = 99999999,
                 UnlimitedCount = true,
                 SptPresetId = preset.Id,
             };
 
-            results.Add(presetAndModsClone);
+            results = results.Union([presetAndModsClone]);
         }
 
         foreach (var (id, item) in dbItems)
@@ -105,15 +105,14 @@ public class RagfairAssortGenerator(
                 continue;
             }
 
-            if (processedArmorItems.Contains(id))
             // Already processed
+            if (processedArmorItems.Contains(id))
             {
                 continue;
             }
 
-            var ragfairAssort = CreateRagfairAssortRootItem(id, id); // tpl and id must be the same so hideout recipe rewards work
-
-            results.Add([ragfairAssort]);
+            var assortItemToAdd = new List<Item> { CreateRagfairAssortRootItem(id, id) }; // tpl and id must be the same so hideout recipe rewards work
+            results = results.Union([assortItemToAdd]);
         }
 
         return results;
diff --git a/Libraries/SPTarkov.Server.Core/Generators/RagfairOfferGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/RagfairOfferGenerator.cs
index efe4f9a8..91c8d458 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/RagfairOfferGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/RagfairOfferGenerator.cs
@@ -362,13 +362,13 @@ public class RagfairOfferGenerator(
 
         stopwatch.Restart();
         var tasks = new List<Task>();
-        foreach (var assortItem in assortItemsToProcess)
+        foreach (var assortItemWithChildren in assortItemsToProcess)
         {
             tasks.Add(
                 Task.Factory.StartNew(() =>
                 {
                     CreateOffersFromAssort(
-                        assortItem,
+                        assortItemWithChildren,
                         replacingExpiredOffers,
                         ragfairConfig.Dynamic
                     );
@@ -725,12 +725,12 @@ public class RagfairOfferGenerator(
     /// <param name="itemDetails"> DB details of first item</param>
     protected void RandomiseOfferItemUpdProperties(
         MongoId userID,
-        List<Item> itemWithMods,
+        IEnumerable<Item> itemWithMods,
         TemplateItem itemDetails
     )
     {
         // Add any missing properties to first item in array
-        AddMissingConditions(itemWithMods[0]);
+        AddMissingConditions(itemWithMods.First());
 
         if (!(profileHelper.IsPlayer(userID) || ragfairServerHelper.IsTrader(userID)))
         {
@@ -781,11 +781,11 @@ public class RagfairOfferGenerator(
     /// <param name="itemDetails"> DB Item details of first item in list </param>
     protected void RandomiseItemCondition(
         MongoId conditionSettingsId,
-        List<Item> itemWithMods,
+        IEnumerable<Item> itemWithMods,
         TemplateItem itemDetails
     )
     {
-        var rootItem = itemWithMods[0];
+        var rootItem = itemWithMods.First();
 
         var itemConditionValues = ragfairConfig.Dynamic.Condition[conditionSettingsId];
         var maxMultiplier = randomUtil.GetDouble(
@@ -827,7 +827,7 @@ public class RagfairOfferGenerator(
         if (itemHelper.IsOfBaseclass(itemDetails.Id, BaseClasses.WEAPON))
         {
             RandomiseWeaponDurability(
-                itemWithMods[0],
+                itemWithMods.First(),
                 itemDetails,
                 maxMultiplier,
                 currentMultiplier
@@ -924,7 +924,7 @@ public class RagfairOfferGenerator(
     /// <param name="currentMultiplier"> Chosen multiplier to use for current durability value </param>
     /// <param name="maxMultiplier"> Chosen multiplier to use for max durability value </param>
     protected void RandomiseArmorDurabilityValues(
-        List<Item> armorWithMods,
+        IEnumerable<Item> armorWithMods,
         double currentMultiplier,
         double maxMultiplier
     )
diff --git a/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/RepeatableQuestRewardGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/RepeatableQuestRewardGenerator.cs
index 068c5545..88f916ff 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/RepeatableQuestRewardGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/RepeatableQuestRewardGenerator.cs
@@ -821,7 +821,7 @@ public class RepeatableQuestRewardGenerator(
         MongoId tpl,
         HashSet<MongoId> itemTplBlacklist,
         HashSet<MongoId> itemTypeBlacklist,
-        List<MongoId>? itemBaseWhitelist = null
+        IEnumerable<MongoId>? itemBaseWhitelist = null
     )
     {
         // Return early if not valid item to give as reward
diff --git a/Libraries/SPTarkov.Server.Core/Generators/ScavCaseRewardGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/ScavCaseRewardGenerator.cs
index 5b51a8a7..e8072f87 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/ScavCaseRewardGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/ScavCaseRewardGenerator.cs
@@ -40,7 +40,7 @@ public class ScavCaseRewardGenerator(
     /// </summary>
     /// <param name="recipeId">recipe of the scav case craft</param>
     /// <returns>Product array</returns>
-    public List<List<Item>> Generate(MongoId recipeId)
+    public IEnumerable<List<Item>> Generate(MongoId recipeId)
     {
         CacheDbItems();
 
@@ -91,13 +91,9 @@ public class ScavCaseRewardGenerator(
             RewardRarity.SuperRare
         );
 
-        var result = new List<List<Item>>();
-        result = result.Concat(commonRewards).ToList();
-        result = result.Concat(rareRewards).ToList();
-        result = result.Concat(superRareRewards).ToList();
-        // TODO: please make this better, how merge 2d Lists
+        var result = commonRewards.Concat(rareRewards).Concat(superRareRewards);
 
-        return result.ToList();
+        return result;
     }
 
     /// <summary>
@@ -365,7 +361,7 @@ public class ScavCaseRewardGenerator(
     /// <param name="rarity">The rarity desired ammo reward is for</param>
     /// <returns>Product array</returns>
     protected List<List<Item>> RandomiseContainerItemRewards(
-        List<TemplateItem> rewardItems,
+        IEnumerable<TemplateItem> rewardItems,
         string rarity
     )
     {
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/HandbookHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/HandbookHelper.cs
index 8e997beb..342301bd 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/HandbookHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/HandbookHelper.cs
@@ -130,7 +130,7 @@ public class HandbookHelper(
     /// </summary>
     /// <param name="items">Items to Sum</param>
     /// <returns></returns>
-    public double GetTemplatePriceForItems(List<Item> items)
+    public double GetTemplatePriceForItems(IEnumerable<Item> items)
     {
         var total = 0D;
         foreach (var item in items)
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/HideoutHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/HideoutHelper.cs
index 35dabc70..c118b110 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/HideoutHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/HideoutHelper.cs
@@ -1510,9 +1510,9 @@ public class HideoutHelper(
         );
 
         // Get all slotted dogtag items
-        var activeDogtags = pmcData
-            .Inventory.Items.Where(item => item?.SlotId?.StartsWith("dogtag") ?? false)
-            .ToList();
+        var activeDogtags = pmcData.Inventory.Items.Where(item =>
+            item?.SlotId?.StartsWith("dogtag") ?? false
+        );
 
         // Calculate bonus percent (apply hideoutManagement bonus)
         var hideoutManagementSkill = pmcData.GetSkillFromProfile(SkillTypes.HideoutManagement);
@@ -1534,7 +1534,7 @@ public class HideoutHelper(
     /// <returns>Combat bonus</returns>
     protected static double GetDogtagCombatSkillBonusPercent(
         PmcData pmcData,
-        List<Item> activeDogtags
+        IEnumerable<Item> activeDogtags
     )
     {
         // Not own dogtag
@@ -1542,12 +1542,12 @@ public class HideoutHelper(
         var result = 0D;
         foreach (var dogtag in activeDogtags)
         {
-            if (dogtag.Upd.Dogtag is null)
+            if (dogtag.Upd?.Dogtag?.AccountId is null)
             {
                 continue;
             }
 
-            if (int.Parse(dogtag.Upd.Dogtag?.AccountId) == pmcData.Aid)
+            if (int.Parse(dogtag.Upd.Dogtag.AccountId) == pmcData.Aid)
             {
                 continue;
             }
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/InRaidHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/InRaidHelper.cs
index 403edee3..8c3bf174 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/InRaidHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/InRaidHelper.cs
@@ -110,7 +110,7 @@ public class InRaidHelper(
     ///     Remove FiR status from items.
     /// </summary>
     /// <param name="items">Items to process</param>
-    protected void RemoveFiRStatusFromItems(List<Item> items)
+    protected void RemoveFiRStatusFromItems(IEnumerable<Item> items)
     {
         var dbItems = databaseService.GetItems();
 
@@ -225,40 +225,38 @@ public class InRaidHelper(
     /// </summary>
     /// <param name="pmcProfile">Profile to get items from</param>
     /// <returns>List of items lost on death</returns>
-    protected List<Item> GetInventoryItemsLostOnDeath(PmcData pmcProfile)
+    protected IEnumerable<Item> GetInventoryItemsLostOnDeath(PmcData pmcProfile)
     {
         var inventoryItems = pmcProfile.Inventory.Items ?? [];
         var equipmentRootId = pmcProfile?.Inventory?.Equipment;
         var questRaidItemContainerId = pmcProfile?.Inventory?.QuestRaidItems;
 
-        return inventoryItems
-            .Where(item =>
+        return inventoryItems.Where(item =>
+        {
+            // Keep items flagged as kept after death
+            if (IsItemKeptAfterDeath(pmcProfile, item))
             {
-                // Keep items flagged as kept after death
-                if (IsItemKeptAfterDeath(pmcProfile, item))
-                {
-                    return false;
-                }
-
-                // Remove normal items or quest raid items
-                if (item.ParentId == equipmentRootId || item.ParentId == questRaidItemContainerId)
-                {
-                    return true;
-                }
-
-                // Pocket items are lost on death
-                // Ensure we don't pick up pocket items from mannequins
-                if (
-                    item.SlotId.StartsWith("pocket")
-                    && pmcProfile.DoesItemHaveRootId(item, pmcProfile.Inventory.Equipment)
-                )
-                {
-                    return true;
-                }
-
                 return false;
-            })
-            .ToList();
+            }
+
+            // Remove normal items or quest raid items
+            if (item.ParentId == equipmentRootId || item.ParentId == questRaidItemContainerId)
+            {
+                return true;
+            }
+
+            // Pocket items are lost on death
+            // Ensure we don't pick up pocket items from mannequins
+            if (
+                item.SlotId.StartsWith("pocket")
+                && pmcProfile.DoesItemHaveRootId(item, pmcProfile.Inventory.Equipment)
+            )
+            {
+                return true;
+            }
+
+            return false;
+        });
     }
 
     /// <summary>
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/InventoryHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/InventoryHelper.cs
index 71cb0eb3..a3ff906e 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/InventoryHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/InventoryHelper.cs
@@ -257,10 +257,10 @@ public class InventoryHelper(
     /// <param name="containerFS2D">Container grid</param>
     /// <param name="itemWithChildren">Item to check fits</param>
     /// <returns>True it fits</returns>
-    public bool CanPlaceItemInContainer(int[,] containerFS2D, List<Item> itemWithChildren)
+    public bool CanPlaceItemInContainer(int[,] containerFS2D, IEnumerable<Item> itemWithChildren)
     {
         // Get x/y size of item
-        var rootItem = itemWithChildren[0];
+        var rootItem = itemWithChildren.First();
         var (sizeX, sizeY) = GetItemSize(rootItem.Template, rootItem.Id, itemWithChildren);
 
         // Look for a place to slot item into
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/ItemHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/ItemHelper.cs
index 44f1f533..6376d052 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/ItemHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/ItemHelper.cs
@@ -67,8 +67,12 @@ public class ItemHelper(
         ItemTpl.BARTER_DOGTAG_USEC_TUE,
         ItemTpl.BARTER_DOGTAG_BEAR_PRESTIGE_1,
         ItemTpl.BARTER_DOGTAG_BEAR_PRESTIGE_2,
+        ItemTpl.BARTER_DOGTAG_BEAR_PRESTIGE_3,
+        ItemTpl.BARTER_DOGTAG_BEAR_PRESTIGE_4,
         ItemTpl.BARTER_DOGTAG_USEC_PRESTIGE_1,
         ItemTpl.BARTER_DOGTAG_USEC_PRESTIGE_2,
+        ItemTpl.BARTER_DOGTAG_USEC_PRESTIGE_3,
+        ItemTpl.BARTER_DOGTAG_USEC_PRESTIGE_4,
     ];
 
     protected static readonly FrozenSet<string> _softInsertIds =
@@ -328,7 +332,7 @@ public class ItemHelper(
     /// <param name="tpl">Item to check base classes of</param>
     /// <param name="baseClassTpls">Base classes to check for</param>
     /// <returns>True if any supplied base classes match</returns>
-    public bool IsOfBaseclasses(MongoId tpl, ICollection<MongoId> baseClassTpls)
+    public bool IsOfBaseclasses(MongoId tpl, IEnumerable<MongoId> baseClassTpls)
     {
         return itemBaseClassService.ItemHasBaseClass(tpl, baseClassTpls);
     }
@@ -729,7 +733,7 @@ public class ItemHelper(
     /// <param name="itemIdToFind">Template id of item to check for</param>
     /// <param name="assort">List of items to check in</param>
     /// <returns>List of children of requested item</returns>
-    public List<Item> FindAndReturnChildrenByAssort(MongoId itemIdToFind, List<Item> assort)
+    public List<Item> FindAndReturnChildrenByAssort(MongoId itemIdToFind, IEnumerable<Item> assort)
     {
         List<Item> list = [];
         var itemIdToFindString = itemIdToFind.ToString();
@@ -901,8 +905,8 @@ public class ItemHelper(
     /// <returns>List of Item objects.</returns>
     public List<Item> FindBarterItems(
         string by,
-        List<Item> itemsToSearch,
-        List<MongoId> desiredBarterItemIds
+        IEnumerable<Item> itemsToSearch,
+        IEnumerable<MongoId> desiredBarterItemIds
     )
     {
         // Find required items to take after buying (handles multiple items)
@@ -933,13 +937,13 @@ public class ItemHelper(
     /// </summary>
     /// <param name="itemWithChildren">Item with mods to update.</param>
     /// <param name="newId">New id to add on children of base item.</param>
-    public void ReplaceRootItemID(List<Item> itemWithChildren, string newId = "")
+    public void ReplaceRootItemID(IEnumerable<Item> itemWithChildren, MongoId newId)
     {
         // original id on base item
-        var oldId = itemWithChildren[0].Id;
+        var oldId = itemWithChildren.First().Id;
 
         // Update base item to use new id
-        itemWithChildren[0].Id = newId;
+        itemWithChildren.First().Id = newId;
 
         // Update all parentIds of items attached to base item to use new id
         foreach (var item in itemWithChildren)
@@ -958,7 +962,7 @@ public class ItemHelper(
     /// <param name="insuredItems"></param>
     public void ReplaceProfileInventoryIds(
         BotBaseInventory inventory,
-        List<InsuredItem>? insuredItems = null
+        IEnumerable<InsuredItem>? insuredItems = null
     )
     {
         // Blacklist
@@ -1028,10 +1032,10 @@ public class ItemHelper(
     /// <param name="insuredItems">Insured items that should not have their IDs replaced</param>
     /// <param name="fastPanel">Quick slot panel</param>
     /// <returns>Items</returns>
-    public List<Item> ReplaceIDs(
-        List<Item> originalItems,
+    public IEnumerable<Item> ReplaceIDs(
+        IEnumerable<Item> originalItems,
         PmcData? pmcData,
-        List<InsuredItem>? insuredItems = null,
+        IEnumerable<InsuredItem>? insuredItems = null,
         Dictionary<string, string>? fastPanel = null
     )
     {
@@ -1090,6 +1094,7 @@ public class ItemHelper(
             }
 
             // Update quickslot id
+            // TODO: i dont think the fast panel key is a mongoid, it should be e.g. "Item4"
             if (pmcData.Inventory.FastPanel.ContainsKey(originalId))
             {
                 pmcData.Inventory.FastPanel[originalId] = newId;
@@ -1105,7 +1110,7 @@ public class ItemHelper(
     ///     Will not flag ammo or currency as FiR
     /// </summary>
     /// <param name="items">The list of items to mark as FiR</param>
-    public void SetFoundInRaid(List<Item> items)
+    public void SetFoundInRaid(IEnumerable<Item> items)
     {
         foreach (var item in items)
         {
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/PrestigeHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/PrestigeHelper.cs
index a996ca37..5a7c4e5b 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/PrestigeHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/PrestigeHelper.cs
@@ -65,7 +65,8 @@ public class PrestigeHelper(
                 }
                 else
                 {
-                    newProfile.CharacterData.PmcData.Skills.Common.Add(skillToCopy);
+                    newProfile.CharacterData.PmcData.Skills.Common =
+                        newProfile.CharacterData.PmcData.Skills.Common.Union([skillToCopy]);
                 }
             }
 
@@ -84,7 +85,8 @@ public class PrestigeHelper(
                 }
                 else
                 {
-                    newProfile.CharacterData.PmcData.Skills.Mastering.Add(skillToCopy);
+                    newProfile.CharacterData.PmcData.Skills.Mastering =
+                        newProfile.CharacterData.PmcData.Skills.Mastering.Union([skillToCopy]);
                 }
             }
         }
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/TraderHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/TraderHelper.cs
index 7eb6a4c5..62be0e89 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/TraderHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/TraderHelper.cs
@@ -225,8 +225,8 @@ public class TraderHelper(
             else
             {
                 pmcData.Info.Bans ??= [];
-                pmcData.Info.Bans.Add(
-                    new Ban { BanType = BanType.RagFair, DateTime = newBanDateTime }
+                pmcData.Info.Bans = pmcData.Info.Bans.Union(
+                    [new Ban { BanType = BanType.RagFair, DateTime = newBanDateTime }]
                 );
             }
         }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/BotBase.cs b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/BotBase.cs
index 1e34bb3c..6fceb70c 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/BotBase.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/BotBase.cs
@@ -208,7 +208,7 @@ public record Info
 
     public MemberCategory? SelectedMemberCategory { get; set; }
 
-    public List<Ban>? Bans { get; set; }
+    public IEnumerable<Ban>? Bans { get; set; }
 
     [JsonPropertyName("lockedMoveCommands")]
     public bool? LockedMoveCommands { get; set; }
@@ -425,11 +425,14 @@ public record BotBaseInventory
     // TODO: key should be EAreaType enum
     public Dictionary<string, MongoId>? HideoutAreaStashes { get; set; } // Key = hideout area key as string
 
+    /// <summary>
+    /// key = "Item4", "Item10"
+    /// </summary>
     [JsonPropertyName("fastPanel")]
     public Dictionary<string, MongoId>? FastPanel { get; set; }
 
     [JsonPropertyName("favoriteItems")]
-    public List<MongoId>? FavoriteItems { get; set; }
+    public IEnumerable<MongoId>? FavoriteItems { get; set; }
 
     [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
     [JsonPropertyName("hideoutCustomizationStashId")]
@@ -441,9 +444,9 @@ public record Skills
     [JsonExtensionData]
     public Dictionary<string, object>? ExtensionData { get; set; }
 
-    public List<CommonSkill> Common { get; set; }
+    public IEnumerable<CommonSkill> Common { get; set; }
 
-    public List<MasterySkill>? Mastering { get; set; }
+    public IEnumerable<MasterySkill>? Mastering { get; set; }
 
     public double? Points { get; set; }
 }
@@ -491,9 +494,9 @@ public record EftStats
     [JsonExtensionData]
     public Dictionary<string, object>? ExtensionData { get; set; }
 
-    public List<string>? CarriedQuestItems { get; set; }
+    public IEnumerable<string>? CarriedQuestItems { get; set; }
 
-    public List<Victim>? Victims { get; set; }
+    public IEnumerable<Victim>? Victims { get; set; }
 
     public double? TotalSessionExperience { get; set; }
 
@@ -510,9 +513,9 @@ public record EftStats
     [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
     public Aggressor? Aggressor { get; set; }
 
-    public List<DroppedItem>? DroppedItems { get; set; }
+    public IEnumerable<DroppedItem>? DroppedItems { get; set; }
 
-    public List<FoundInRaidItem>? FoundInRaidItems { get; set; }
+    public IEnumerable<FoundInRaidItem>? FoundInRaidItems { get; set; }
 
     public DamageHistory? DamageHistory { get; set; }
 
@@ -588,7 +591,7 @@ public record SessionCounters
     [JsonExtensionData]
     public Dictionary<string, object>? ExtensionData { get; set; }
 
-    public List<CounterKeyValue>? Items { get; set; }
+    public IEnumerable<CounterKeyValue>? Items { get; set; }
 }
 
 public record OverallCounters
@@ -604,7 +607,7 @@ public record CounterKeyValue
     [JsonExtensionData]
     public Dictionary<string, object>? ExtensionData { get; set; }
 
-    public List<string>? Key { get; set; }
+    public IEnumerable<string>? Key { get; set; }
 
     public double? Value { get; set; }
 }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Eft/Inventory/AddItemsDirectRequest.cs b/Libraries/SPTarkov.Server.Core/Models/Eft/Inventory/AddItemsDirectRequest.cs
index cc2db11c..a4b2c1a9 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Eft/Inventory/AddItemsDirectRequest.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Eft/Inventory/AddItemsDirectRequest.cs
@@ -12,7 +12,7 @@ public record AddItemsDirectRequest
     ///     Item and child mods to add to player inventory
     /// </summary>
     [JsonPropertyName("itemsWithModsToAdd")]
-    public List<List<Item>>? ItemsWithModsToAdd { get; set; }
+    public IEnumerable<List<Item>>? ItemsWithModsToAdd { get; set; }
 
     [JsonPropertyName("foundInRaid")]
     public bool? FoundInRaid { get; set; }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Eft/PresetBuild/PresetBuildActionRequestData.cs b/Libraries/SPTarkov.Server.Core/Models/Eft/PresetBuild/PresetBuildActionRequestData.cs
index 5cd15e6f..657776fa 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Eft/PresetBuild/PresetBuildActionRequestData.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Eft/PresetBuild/PresetBuildActionRequestData.cs
@@ -26,5 +26,5 @@ public record PresetBuildActionRequestData : IRequestData
     public string? Root { get; set; }
 
     [JsonPropertyName("Items")]
-    public List<Item>? Items { get; set; }
+    public IEnumerable<Item>? Items { get; set; }
 }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/ModToSpawnRequest.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/ModToSpawnRequest.cs
index 37471983..9ade62a7 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/ModToSpawnRequest.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/ModToSpawnRequest.cs
@@ -48,7 +48,7 @@ public record ModToSpawnRequest
     ///     List with only weapon tpl in it, ready for mods to be added
     /// </summary>
     [JsonPropertyName("weapon")]
-    public List<Item>? Weapon { get; set; }
+    public IEnumerable<Item>? Weapon { get; set; }
 
     /// <summary>
     ///     Ammo tpl to use if slot requires a cartridge to be added (e.g. mod_magazine)
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/QuestConfig.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/QuestConfig.cs
index 78797caa..e51703e3 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/QuestConfig.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/QuestConfig.cs
@@ -326,13 +326,13 @@ public record TraderWhitelist
     ///     Quest types this trader can provide: Completion/Exploration/Elimination.
     /// </summary>
     [JsonPropertyName("questTypes")]
-    public required List<string> QuestTypes { get; set; }
+    public required HashSet<string> QuestTypes { get; set; }
 
     /// <summary>
     ///     Item categories that the reward can be
     /// </summary>
     [JsonPropertyName("rewardBaseWhitelist")]
-    public required List<MongoId> RewardBaseWhitelist { get; set; }
+    public required IEnumerable<MongoId> RewardBaseWhitelist { get; set; }
 
     /// <summary>
     ///     Can this reward be a weapon?
diff --git a/Libraries/SPTarkov.Server.Core/Services/FenceService.cs b/Libraries/SPTarkov.Server.Core/Services/FenceService.cs
index 377c1a99..b17cef34 100644
--- a/Libraries/SPTarkov.Server.Core/Services/FenceService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/FenceService.cs
@@ -1364,15 +1364,13 @@ public class FenceService(
             if (!randomUtil.GetChance100(plateExistsChance))
             {
                 // Remove plate from armor
-                armorItemAndMods = armorItemAndMods
-                    .Where(item =>
-                        !string.Equals(
-                            item.SlotId,
-                            plateSlot.Name,
-                            StringComparison.CurrentCultureIgnoreCase
-                        )
+                armorItemAndMods = armorItemAndMods.Where(item =>
+                    !string.Equals(
+                        item.SlotId,
+                        plateSlot.Name,
+                        StringComparison.CurrentCultureIgnoreCase
                     )
-                    .ToList();
+                );
 
                 continue;
             }
diff --git a/Libraries/SPTarkov.Server.Core/Services/ItemBaseClassService.cs b/Libraries/SPTarkov.Server.Core/Services/ItemBaseClassService.cs
index 65bd2116..cad84e03 100644
--- a/Libraries/SPTarkov.Server.Core/Services/ItemBaseClassService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/ItemBaseClassService.cs
@@ -68,7 +68,7 @@ public class ItemBaseClassService(
     /// <param name="itemTpl"> ItemTpl item to check base classes of </param>
     /// <param name="baseClasses"> BaseClass base class to check for </param>
     /// <returns> true if item inherits from base class passed in </returns>
-    public bool ItemHasBaseClass(MongoId itemTpl, ICollection<MongoId> baseClasses)
+    public bool ItemHasBaseClass(MongoId itemTpl, IEnumerable<MongoId> baseClasses)
     {
         if (!_cacheGenerated)
         {
diff --git a/Libraries/SPTarkov.Server.Core/Services/LocationLifecycleService.cs b/Libraries/SPTarkov.Server.Core/Services/LocationLifecycleService.cs
index ae611951..cd4f3296 100644
--- a/Libraries/SPTarkov.Server.Core/Services/LocationLifecycleService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/LocationLifecycleService.cs
@@ -960,12 +960,12 @@ public class LocationLifecycleService(
         // Must occur AFTER killer messages have been sent
         matchBotDetailsCacheService.ClearCache();
 
-        var roles = new List<string> { "pmcbear", "pmcusec" };
+        var roles = new HashSet<string> { "pmcbear", "pmcusec" };
 
-        var victims = postRaidProfile
-            .Stats.Eft.Victims.Where(victim => roles.Contains(victim.Role.ToLowerInvariant()))
-            .ToList();
-        if (victims?.Count > 0)
+        var victims = postRaidProfile.Stats.Eft.Victims.Where(victim =>
+            roles.Contains(victim.Role.ToLowerInvariant())
+        );
+        if (victims is not null && victims.Any())
         // Player killed PMCs, send some mail responses to them
         {
             pmcChatResponseService.SendVictimResponse(sessionId, victims, serverPmcProfile);
@@ -1233,7 +1233,7 @@ public class LocationLifecycleService(
     ///     Reset the skill points earned in a raid to 0, ready for next raid
     /// </summary>
     /// <param name="commonSkills"> Profile common skills to update </param>
-    protected void ResetSkillPointsEarnedDuringRaid(List<CommonSkill> commonSkills)
+    protected void ResetSkillPointsEarnedDuringRaid(IEnumerable<CommonSkill> commonSkills)
     {
         foreach (var skill in commonSkills)
         {
diff --git a/Libraries/SPTarkov.Server.Core/Services/PmcChatResponseService.cs b/Libraries/SPTarkov.Server.Core/Services/PmcChatResponseService.cs
index 20e30949..0bd9bea8 100644
--- a/Libraries/SPTarkov.Server.Core/Services/PmcChatResponseService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/PmcChatResponseService.cs
@@ -35,7 +35,11 @@ public class PmcChatResponseService(
     /// <param name="sessionId"> Session ID </param>
     /// <param name="pmcVictims"> List of bots killed by player </param>
     /// <param name="pmcData"> Player profile </param>
-    public void SendVictimResponse(MongoId sessionId, List<Victim> pmcVictims, PmcData pmcData)
+    public void SendVictimResponse(
+        MongoId sessionId,
+        IEnumerable<Victim> pmcVictims,
+        PmcData pmcData
+    )
     {
         foreach (var victim in pmcVictims)
         {