diff --git a/Content.Tests/DMProject/Tests/List/ListIndexToKey.dm b/Content.Tests/DMProject/Tests/List/ListIndexToKey.dm
new file mode 100644
index 0000000000..37ddbc713d
--- /dev/null
+++ b/Content.Tests/DMProject/Tests/List/ListIndexToKey.dm
@@ -0,0 +1,13 @@
+/proc/RunTest()
+	var/list/A = list("thing")
+	ASSERT(A[1] == "thing")
+	
+	A["thing"] = 6
+	ASSERT(A["thing"] == 6)
+
+	var/list/L = list()
+	for(var/i in 1 to 5)
+		L.Add("[i]")
+		L["[i]"] = "item [i]"
+	ASSERT(length(L) == 5)
+	ASSERT(L["3"] == "item 3")
diff --git a/OpenDreamRuntime/Objects/Types/DreamAssocList.cs b/OpenDreamRuntime/Objects/Types/DreamAssocList.cs
index 8b84d4aa53..bfed4e2a65 100644
--- a/OpenDreamRuntime/Objects/Types/DreamAssocList.cs
+++ b/OpenDreamRuntime/Objects/Types/DreamAssocList.cs
@@ -119,4 +119,16 @@ public bool ContainsValue(DreamValue value) {
         return _values.ContainsKey(value);
     }
 
+    public override DreamValue OperatorAppend(DreamValue b) {
+        if (b.TryGetValueAsDreamList(out var bList)) {
+            foreach (var value in bList.EnumerateValues()) {
+                AddValue(value);
+            }
+        } else {
+            AddValue(b);
+        }
+
+        return new(this);
+    }
+
 }
diff --git a/OpenDreamRuntime/Objects/Types/DreamList.cs b/OpenDreamRuntime/Objects/Types/DreamList.cs
index 7dc0e2e830..bf15b0906b 100644
--- a/OpenDreamRuntime/Objects/Types/DreamList.cs
+++ b/OpenDreamRuntime/Objects/Types/DreamList.cs
@@ -18,6 +18,10 @@ public class DreamList : DreamObject, IDreamList {
 
     public virtual bool IsAssociative => _associativeValues is { Count: > 0 };
 
+    /// <summary>
+    /// Looks up the key to find the index
+    /// </summary>
+    private readonly Dictionary<DreamValue, int> _reverseLookup = [];
     private readonly List<DreamValue> _values;
     private Dictionary<DreamValue, DreamValue>? _associativeValues;
 
@@ -29,6 +33,12 @@ public DreamList(DreamObjectDefinition listDef, int size) : base(listDef) {
         if (size >= DreamManager.ListPoolThreshold && ListPool.TryPop(out var poppedValues)) {
             _values = poppedValues;
             _values.EnsureCapacity(size);
+            foreach (var value in poppedValues) {
+                if (!_reverseLookup.TryAdd(value, 1)) {
+                    _reverseLookup[value] += 1;
+                }
+            }
+
         } else {
             _values = new List<DreamValue>(size);
         }
@@ -39,6 +49,11 @@ public DreamList(DreamObjectDefinition listDef, int size) : base(listDef) {
     /// </summary>
     public DreamList(DreamObjectDefinition listDef, List<DreamValue> values, Dictionary<DreamValue, DreamValue>? associativeValues) : base(listDef) {
         _values = values;
+        foreach (var value in values) {
+            if (!_reverseLookup.TryAdd(value, 1)) {
+                _reverseLookup[value] += 1;
+            }
+        }
         _associativeValues = associativeValues;
 
         #if TOOLS
@@ -172,13 +187,31 @@ public virtual DreamValue GetValue(DreamValue key) {
 
     public virtual void SetValue(DreamValue key, DreamValue value, bool allowGrowth = false) {
         if (key.TryGetValueAsInteger(out int keyInteger)) {
-            if (allowGrowth && keyInteger == _values.Count + 1) {
+            var index = _values.Count + 1;
+            if (allowGrowth && keyInteger == index) {
                 _values.Add(value);
+
+                if (!_reverseLookup.TryAdd(value, 1)) {
+                    _reverseLookup[value] += 1;
+                }
             } else {
+                var oldValue = _values[keyInteger - 1];
+                var rLCount = _reverseLookup[oldValue] -= 1;
+                if(rLCount <= 0) {
+                    _reverseLookup.Remove(oldValue);
+                }
+
                 _values[keyInteger - 1] = value;
+
+                if (!_reverseLookup.TryAdd(value, 1)) {
+                    _reverseLookup[value] += 1;
+                }
+
             }
         } else {
-            if (!ContainsValue(key)) _values.Add(key);
+            if (_reverseLookup.TryAdd(key, 1)) {
+                _values.Add(key);
+            }
 
             _associativeValues ??= new Dictionary<DreamValue, DreamValue>(1);
             _associativeValues[key] = value;
@@ -191,6 +224,13 @@ public virtual void RemoveValue(DreamValue value) {
         int valueIndex = _values.LastIndexOf(value);
 
         if (valueIndex != -1) {
+            if (_reverseLookup.ContainsKey(value)) {
+                var rLCount = _reverseLookup[value] -= 1;
+                if (rLCount <= 0) {
+                    _reverseLookup.Remove(value);
+                }
+            }
+
             _associativeValues?.Remove(value);
             _values.RemoveAt(valueIndex);
         }
@@ -199,18 +239,17 @@ public virtual void RemoveValue(DreamValue value) {
     }
 
     public virtual void AddValue(DreamValue value) {
-        _values.Add(value);
+        _values.Add(value); 
+        if (!_reverseLookup.TryAdd(value, 1)) {
+            _reverseLookup[value] += 1;
+        }
+
         UpdateTracyContentsMemory();
     }
 
     //Does not include associations
     public virtual bool ContainsValue(DreamValue value) {
-        for (int i = 0; i < _values.Count; i++) {
-            if (_values[i].Equals(value))
-                return true;
-        }
-
-        return false;
+        return _reverseLookup.ContainsKey(value);
     }
 
     public virtual bool ContainsKey(DreamValue value) {
@@ -220,6 +259,8 @@ public virtual bool ContainsKey(DreamValue value) {
     public virtual int FindValue(DreamValue value, int start = 1, int end = 0) {
         if (end == 0 || end > _values.Count) end = _values.Count + 1;
 
+        if(!ContainsValue(value)) return 0;
+        
         for (int i = start; i < end; i++) {
             if (_values[i - 1].Equals(value)) return i;
         }
@@ -235,14 +276,30 @@ public virtual void Cut(int start = 1, int end = 0) {
                 _associativeValues.Remove(_values[i - 1]);
         }
 
-        if (end > start)
-            _values.RemoveRange(start - 1, end - start);
+        if (end > start) {
+            var index = start - 1;
+            var len = end - start;
+            var elements = _values.GetRange(index, len);
+
+            foreach (var element in elements) {
+                var rlCache = _reverseLookup[element] -= 1;
+
+                if (rlCache <= 0) {
+                    _reverseLookup.Remove(element);
+                }
+            }
+
+            _values.RemoveRange(index, len);
+        }
 
         UpdateTracyContentsMemory();
     }
 
     public void Insert(int index, DreamValue value) {
         _values.Insert(index - 1, value);
+        if (!_reverseLookup.TryAdd(value, 1)) {
+            _reverseLookup[value] += 1;
+        }
         UpdateTracyContentsMemory();
     }
 
@@ -652,6 +709,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
             yield return new(verb);
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void SetValue(DreamValue key, DreamValue value, bool allowGrowth = false) {
         throw new Exception("Cannot set the values of a verbs list");
     }
@@ -716,6 +783,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
         }
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void SetValue(DreamValue key, DreamValue value, bool allowGrowth = false) {
         throw new Exception("Cannot set the values of a verbs list");
     }
@@ -790,6 +867,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
         }
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void Cut(int start = 1, int end = 0) {
         _atomManager.UpdateAppearance(_owner, appearance => {
             var overlaysList = GetOverlaysList(appearance);
@@ -907,6 +994,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
             yield return new(visContent);
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void Cut(int start = 1, int end = 0) {
         int count = _visContents.Count + 1;
         if (end == 0 || end > count) end = count;
@@ -1064,6 +1161,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
         }
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void SetValue(DreamValue key, DreamValue value, bool allowGrowth = false) {
         if (!value.TryGetValueAsDreamObject<DreamObjectFilter>(out var filterObject) && !value.IsNull)
             throw new Exception($"Cannot set value of filter list to {value}");
@@ -1212,6 +1319,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
         return _imageObjects;
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void SetValue(DreamValue key, DreamValue value, bool allowGrowth = false) {
         throw new Exception("Cannot write to an index of a client images list");
     }
@@ -1275,6 +1392,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
         return AtomManager.EnumerateAtoms().Select(atom => new DreamValue(atom));
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void SetValue(DreamValue key, DreamValue value, bool allowGrowth = false) {
         throw new Exception("Cannot set the value of world contents list");
     }
@@ -1318,6 +1445,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
             yield return new(movable);
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void SetValue(DreamValue key, DreamValue value, bool allowGrowth = false) {
         throw new Exception("Cannot set an index of turf contents list");
     }
@@ -1386,6 +1523,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
         }
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void SetValue(DreamValue key, DreamValue value, bool allowGrowth = false) {
         throw new Exception("Cannot set an index of area contents list");
     }
@@ -1537,6 +1684,16 @@ public override IEnumerable<DreamValue> EnumerateValues() {
             yield return state.GetArguments()[i];
     }
 
+    public override bool ContainsValue(DreamValue value) {
+        foreach (var containedVal in EnumerateValues()) {
+            if (value.Equals(containedVal)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public override void SetValue(DreamValue key, DreamValue value, bool allowGrowth = false) {
         if (!key.TryGetValueAsInteger(out var index))
             throw new Exception($"Invalid index into args list: {key}");