diff --git a/Abstracts/CustomAncientModel.cs b/Abstracts/CustomAncientModel.cs
index e37c10f3..3c3bcfb7 100644
--- a/Abstracts/CustomAncientModel.cs
+++ b/Abstracts/CustomAncientModel.cs
@@ -23,7 +23,9 @@ public CustomAncientModel(bool autoAdd = true, bool logDialogueLoad = false)
     public virtual List<(string, string)>? Localization => null;
 
     /// <summary>
-    /// Suggested to check act.ActNumber == 2 or 3.
+    /// Suggested to check act.ActNumber == 1 or 2 or 3.
+    ///
+    /// If you want the Ancient to spawn in Act 1, additionally override IsAct1Ancient and return true.
     ///
     /// If you are overriding ShouldForceSpawn, you should override this and return false.
     /// </summary>
@@ -39,6 +41,12 @@ public CustomAncientModel(bool autoAdd = true, bool logDialogueLoad = false)
     /// <returns></returns>
     public virtual bool ShouldForceSpawn(ActModel act, AncientEventModel? rngChosenAncient) => false;
     
+    /// <summary>
+    /// Return true if this should be an Act 1 Ancient.
+    /// </summary>
+    /// <returns></returns>
+    public virtual bool IsAct1Ancient() => false;
+    
     /// <summary>
     /// Set up a new OptionPools with 1, 2, or 3 pools using MakePool for each pool.
     /// If there is 1 pool, all ancient options will be chosen randomly from this pool.
diff --git a/Patches/Content/ContentPatches.cs b/Patches/Content/ContentPatches.cs
index 8dc8c0a5..34b8ec48 100644
--- a/Patches/Content/ContentPatches.cs
+++ b/Patches/Content/ContentPatches.cs
@@ -1,4 +1,6 @@
 using System.Reflection;
+using System.Reflection.Emit;
+using System.Runtime.CompilerServices;
 using System.Text;
 using BaseLib.Abstracts;
 using BaseLib.Extensions;
@@ -10,6 +12,7 @@
 using MegaCrit.Sts2.Core.Modding;
 using MegaCrit.Sts2.Core.Models;
 using MegaCrit.Sts2.Core.Models.Acts;
+using MegaCrit.Sts2.Core.Models.Events;
 using MegaCrit.Sts2.Core.Models.Relics;
 using MegaCrit.Sts2.Core.Random;
 using MegaCrit.Sts2.Core.Rooms;
@@ -290,6 +293,227 @@ static void ForceAncientToSpawn(ActModel __instance)
     }
 }
 
+[HarmonyPatch]
+static class AddAct1AncientsToModelPool
+{
+    [HarmonyTargetMethods]
+    public static IEnumerable<MethodBase> TargetMethods()
+    {
+        MethodInfo abstractMethod = AccessTools.DeclaredMethod(
+            typeof(ActModel),
+            nameof(ActModel.GetUnlockedAncients),
+            [typeof(UnlockState)]);
+
+        return AccessTools.AllTypes()
+            .Where(type =>
+                type != typeof(ActModel) &&
+                typeof(ActModel).IsAssignableFrom(type))
+            .Select(type => AccessTools.Method(
+                type,
+                nameof(ActModel.GetUnlockedAncients),
+                [typeof(UnlockState)]))
+            .Where(method =>
+                method is not null &&
+                !method.IsAbstract &&
+                method.GetBaseDefinition() == abstractMethod)
+            .Distinct();
+    }
+
+    [HarmonyPostfix]
+    private static IEnumerable<AncientEventModel> Postfix(
+        IEnumerable<AncientEventModel> ancients,
+        ActModel __instance)
+    {
+        if (__instance.ActNumber() != 1)
+            return ancients;
+
+        List<AncientEventModel> result = ancients.ToList();
+
+        foreach (CustomAncientModel ancient in CustomContentDictionary.CustomAncients)
+        {
+            if (ancient.IsAct1Ancient() && ancient.IsValidForAct(__instance))
+            {
+                result.Add(ancient);
+            }
+        }
+
+        return result;
+    }
+}
+
+/// <summary>
+/// In base game the check for Neow is hardcoded. This patch is needed to properly set up the run.
+/// </summary>
+[HarmonyPatch]
+public static class AddAct1Ancients_NeowChecks
+{
+    private static readonly MethodInfo IsNeowLikeMethod =
+        AccessTools.Method(
+            typeof(AddAct1Ancients_NeowChecks),
+            nameof(IsNeowLike))
+        ?? throw new MissingMethodException(
+            nameof(AddAct1Ancients_NeowChecks),
+            nameof(IsNeowLike));
+
+    /// <summary>
+    ///     BeforeEventStarted is async, so its actual body is inside the
+    ///     compiler-generated IAsyncStateMachine.MoveNext method.
+    /// </summary>
+    [HarmonyTargetMethod]
+    private static MethodBase TargetMethod()
+    {
+        MethodInfo beforeEventStarted =
+            AccessTools.Method(
+                typeof(AncientEventModel),
+                "BeforeEventStarted",
+                [typeof(bool)])
+            ?? throw new MissingMethodException(
+                typeof(AncientEventModel).FullName,
+                "BeforeEventStarted");
+
+        AsyncStateMachineAttribute stateMachineAttribute =
+            beforeEventStarted.GetCustomAttribute<AsyncStateMachineAttribute>()
+            ?? throw new InvalidOperationException(
+                "BeforeEventStarted does not have an AsyncStateMachineAttribute.");
+
+        return AccessTools.Method(
+                   stateMachineAttribute.StateMachineType,
+                   nameof(IAsyncStateMachine.MoveNext))
+               ?? throw new MissingMethodException(
+                   stateMachineAttribute.StateMachineType.FullName,
+                   nameof(IAsyncStateMachine.MoveNext));
+    }
+
+    [HarmonyTranspiler]
+    private static IEnumerable<CodeInstruction> Transpiler(
+        IEnumerable<CodeInstruction> instructions)
+    {
+        int replacements = 0;
+
+        foreach (CodeInstruction instruction in instructions)
+        {
+            if (instruction.opcode == OpCodes.Isinst &&
+                instruction.operand is Type checkedType &&
+                checkedType == typeof(Neow))
+            {
+                /*
+                 * Original:
+                 *
+                 *     ancient
+                 *     isinst Neow
+                 *
+                 * Replacement:
+                 *
+                 *     ancient
+                 *     dup
+                 *     isinst Neow
+                 *     call IsNeowLike
+                 *
+                 * Stack:
+                 *
+                 *     ancient
+                 *     ancient, ancient
+                 *     ancient, originalResult
+                 *     extendedResult
+                 *
+                 * The original `isinst Neow` instruction remains unchanged,
+                 * so transpilers running after this one can still find it.
+                 */
+                var duplicateInstruction =
+                    new CodeInstruction(OpCodes.Dup);
+
+                var extendResultInstruction =
+                    new CodeInstruction(
+                        OpCodes.Call,
+                        IsNeowLikeMethod);
+
+                /*
+                 * A branch targeting the original isinst must execute the
+                 * inserted dup first.
+                 */
+                instruction.MoveLabelsTo(duplicateInstruction);
+
+                /*
+                 * Keep the complete inserted sequence inside the same
+                 * exception region:
+                 *
+                 * - beginning boundaries go on the first instruction;
+                 * - ending boundaries go on the final instruction.
+                 */
+                foreach (ExceptionBlock block in instruction.ExtractBlocks())
+                {
+                    if (block.blockType == ExceptionBlockType.EndExceptionBlock)
+                    {
+                        extendResultInstruction.blocks.Add(block);
+                    }
+                    else
+                    {
+                        duplicateInstruction.blocks.Add(block);
+                    }
+                }
+
+                yield return duplicateInstruction;
+                yield return instruction;
+                yield return extendResultInstruction;
+
+                replacements++;
+                continue;
+            }
+
+            yield return instruction;
+        }
+
+        if (replacements != 2)
+        {
+            throw new InvalidOperationException(
+                $"Expected to extend 2 Neow checks in " +
+                $"{nameof(AncientEventModel)}.BeforeEventStarted, " +
+                $"but extended {replacements}. The game method or another " +
+                $"transpiler may have changed.");
+        }
+    }
+
+    /// <summary>
+    ///     Extends the result of the original `isinst Neow` instruction.
+    ///     A non-null original result is retained. This also composes with
+    ///     another transpiler that replaces the preserved isinst with a
+    ///     compatible object-to-object check.
+    /// </summary>
+    private static object? IsNeowLike(
+        object? ancient,
+        object? originalResult)
+    {
+        return originalResult
+               ?? (CustomContentDictionary.CustomAncients.Any(customAncient =>
+                       customAncient.IsAct1Ancient()
+                       && customAncient.GetType().IsInstanceOfType(ancient))
+                   ? ancient
+                   : null);
+    }
+}
+
+/// <summary>
+/// Ensures that Neow is always used as the Act 1 Ancient in Custom and Daily runs.
+///
+/// Earlier patches cannot access the RunState, and their owner is always null, so this behavior must be applied by
+/// patching RunManager.GenerateRooms.
+///
+/// If the run has at least one modifier, this patch overrides the Act 1 Ancient with Neow.
+/// </summary>
+[HarmonyPatch(typeof(RunManager), nameof(RunManager.GenerateRooms))]
+class AddAct1Ancients_AlwaysUseNeowInCustomRuns
+{
+    [HarmonyPostfix]
+    private static void Postfix(RunManager __instance)
+    {
+        if (__instance.State is { Modifiers.Count: > 0, Acts.Count: > 0 } &&
+            __instance.State.Acts[0].Ancient is not Neow)
+        {
+            __instance.State.Acts[0]._rooms.Ancient = ModelDb.Event<Neow>();
+        }
+    }
+}
+
 [HarmonyPatch(typeof(ModelDb), nameof(ModelDb.AllSharedEvents), MethodType.Getter)]
 class CustomSharedEvents
 {