diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index f9baef23..8f27733a 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -5800,6 +5800,17 @@ public sealed class GameWindow : IDisposable
                     .DumpEntitySourceIds.Contains(stab.Id);
                 int dumpSetupParts = -1, dumpPlacementFrames = -1, dumpFlattened = -1, dumpDropped = 0;
 
+                // #136: skip an EDITOR-ONLY placement marker. Such a dat object degrades to
+                // nothing (GfxObj id 0) at any runtime distance, so retail's distance-based
+                // degrade (CPhysicsPart::UpdateViewerDistance) never draws it — only the
+                // WorldBuilder editor shows it at the origin. acdream's render path came from
+                // WB (no distance LOD), so without this skip it draws the marker forever (the
+                // red/green dungeon "cone"). Bare-GfxObj stabs are checked here; Setup stabs
+                // skip per-part below (a Setup that is ALL markers drops via meshRefs.Count==0).
+                if ((stab.Id & 0xFF000000u) == 0x01000000u
+                    && AcDream.Core.Meshing.GfxObjDegradeResolver.IsRuntimeHiddenMarker(_dats, stab.Id))
+                    continue;
+
                 var meshRefs = new List<AcDream.Core.World.MeshRef>();
                 var interiorBounds = new AcDream.Core.Meshing.LocalBoundsAccumulator();
                 if ((stab.Id & 0xFF000000u) == 0x01000000u)
@@ -5833,6 +5844,12 @@ public sealed class GameWindow : IDisposable
                         }
                         foreach (var mr in flat)
                         {
+                            // #136: skip an editor-only marker PART (retail hides it at runtime
+                            // distance). The #136 dungeon "cone" is Setup 0x02000C39 whose sole
+                            // part GfxObj 0x010028CA is such a marker — skipping it empties
+                            // meshRefs and the whole stab drops below.
+                            if (AcDream.Core.Meshing.GfxObjDegradeResolver.IsRuntimeHiddenMarker(_dats, mr.GfxObjId))
+                                continue;
                             var gfx = _dats.Get<DatReaderWriter.DBObjs.GfxObj>(mr.GfxObjId);
                             if (gfx is null)
                             {
diff --git a/src/AcDream.Core/Meshing/GfxObjDegradeResolver.cs b/src/AcDream.Core/Meshing/GfxObjDegradeResolver.cs
index c8d38bf7..c9c2bedd 100644
--- a/src/AcDream.Core/Meshing/GfxObjDegradeResolver.cs
+++ b/src/AcDream.Core/Meshing/GfxObjDegradeResolver.cs
@@ -141,4 +141,53 @@ public static class GfxObjDegradeResolver
         resolvedGfxObj = closeGfxObj;
         return true;
     }
+
+    /// <summary>
+    /// True when a GfxObj is an EDITOR-ONLY placement marker that retail's distance-based
+    /// degrade hides at any runtime distance. Such a marker's closest degrade slot is visible
+    /// ONLY at distance 0 (<c>Degrades[0].MaxDist == 0</c>) and the table degrades to GfxObj
+    /// id 0 (= nothing) at real distance. Retail
+    /// (<c>CPhysicsPart::UpdateViewerDistance</c> 0x0050E030 → <c>Draw</c> 0x0050D7A0 picks
+    /// <c>gfxobj[deg_level]</c> by viewer distance) therefore never draws it in the live
+    /// client — only WorldBuilder shows it at the editor origin. acdream has no per-frame
+    /// distance-LOD (the resolver above always returns slot 0), so without this check it
+    /// renders the marker mesh forever — the #136 dungeon "red/green cone" (Setup 0x02000C39
+    /// / GfxObj 0x010028CA, whose degrade table 0x11000118 is {slot0 Id=mesh MaxDist=0,
+    /// slot1 Id=0 MaxDist=FLT_MAX}). Callers that hydrate static geometry (always viewed at
+    /// distance &gt; 0) skip such GfxObjs.
+    /// </summary>
+    public static bool IsRuntimeHiddenMarker(DatCollection dats, uint gfxObjId)
+        => IsRuntimeHiddenMarker(
+            id => dats.Get<GfxObj>(id),
+            id => dats.Get<GfxObjDegradeInfo>(id),
+            gfxObjId);
+
+    /// <summary>Loader-callback overload of <see cref="IsRuntimeHiddenMarker(DatCollection, uint)"/>.</summary>
+    public static bool IsRuntimeHiddenMarker(
+        Func<uint, GfxObj?> getGfxObj,
+        Func<uint, GfxObjDegradeInfo?> getDegradeInfo,
+        uint gfxObjId)
+    {
+        var gfxObj = getGfxObj(gfxObjId);
+        if (gfxObj is null
+            || !gfxObj.Flags.HasFlag(GfxObjFlags.HasDIDDegrade)
+            || gfxObj.DIDDegrade == 0)
+            return false;
+
+        var info = getDegradeInfo(gfxObj.DIDDegrade);
+        if (info is null || info.Degrades.Count == 0)
+            return false;
+
+        // Closest slot visible only at distance exactly 0 = editor-only placement marker.
+        bool firstSlotEditorOnly = info.Degrades[0].MaxDist == 0f;
+        if (!firstSlotEditorOnly)
+            return false;
+
+        // ...and the table degrades to NOTHING (id 0) at real distance — confirms it
+        // becomes invisible at runtime rather than LOD-swapping to a real mesh.
+        foreach (var d in info.Degrades)
+            if ((uint)d.Id == 0u)
+                return true;
+        return false;
+    }
 }
diff --git a/tests/AcDream.Core.Tests/Meshing/GfxObjDegradeResolverTests.cs b/tests/AcDream.Core.Tests/Meshing/GfxObjDegradeResolverTests.cs
index 54dc9c28..887bd340 100644
--- a/tests/AcDream.Core.Tests/Meshing/GfxObjDegradeResolverTests.cs
+++ b/tests/AcDream.Core.Tests/Meshing/GfxObjDegradeResolverTests.cs
@@ -179,4 +179,89 @@ public class GfxObjDegradeResolverTests
         Assert.Equal(baseId, resolvedId);
         Assert.Null(resolvedGfx);
     }
+
+    // ── #136: editor-only placement marker detection ──────────────────────────
+
+    /// <summary>
+    /// The #136 dungeon "cone": its degrade table's slot 0 is visible ONLY at distance 0
+    /// (MaxDist=0) and the table degrades to GfxObj id 0 (= nothing) at real distance.
+    /// Retail's distance degrade never draws it in the live client; we must skip it.
+    /// </summary>
+    [Fact]
+    public void IsRuntimeHiddenMarker_EditorMarkerDegradingToNothing_True()
+    {
+        const uint markerGfx = 0x010028CAu;
+        const uint degradeId = 0x11000118u;
+        var gfx = new GfxObj { Flags = GfxObjFlags.HasDIDDegrade, DIDDegrade = degradeId };
+        var info = new GfxObjDegradeInfo
+        {
+            Degrades =
+            {
+                new GfxObjInfo { Id = markerGfx, MaxDist = 0f },
+                new GfxObjInfo { Id = 0u, MaxDist = float.MaxValue },
+            },
+        };
+        var gfxObjs = new Dictionary<uint, GfxObj> { [markerGfx] = gfx };
+        var infos = new Dictionary<uint, GfxObjDegradeInfo> { [degradeId] = info };
+
+        Assert.True(GfxObjDegradeResolver.IsRuntimeHiddenMarker(
+            id => gfxObjs.GetValueOrDefault(id), id => infos.GetValueOrDefault(id), markerGfx));
+    }
+
+    /// <summary>A real LOD object — slot 0 visible out to a real distance (MaxDist&gt;0) —
+    /// is NOT a marker, even though it degrades further.</summary>
+    [Fact]
+    public void IsRuntimeHiddenMarker_NormalLodObject_False()
+    {
+        const uint baseId = 0x01000055u;
+        const uint degradeId = 0x110006D0u;
+        var gfx = new GfxObj { Flags = GfxObjFlags.HasDIDDegrade, DIDDegrade = degradeId };
+        var info = new GfxObjDegradeInfo
+        {
+            Degrades =
+            {
+                new GfxObjInfo { Id = 0x01001795u, MaxDist = 25f },
+                new GfxObjInfo { Id = 0u, MaxDist = float.MaxValue },
+            },
+        };
+        var gfxObjs = new Dictionary<uint, GfxObj> { [baseId] = gfx };
+        var infos = new Dictionary<uint, GfxObjDegradeInfo> { [degradeId] = info };
+
+        Assert.False(GfxObjDegradeResolver.IsRuntimeHiddenMarker(
+            id => gfxObjs.GetValueOrDefault(id), id => infos.GetValueOrDefault(id), baseId));
+    }
+
+    /// <summary>No degrade table at all → not a marker.</summary>
+    [Fact]
+    public void IsRuntimeHiddenMarker_NoDegradeTable_False()
+    {
+        const uint baseId = 0x01001212u;
+        var gfx = new GfxObj { Flags = 0, DIDDegrade = 0 };
+        var gfxObjs = new Dictionary<uint, GfxObj> { [baseId] = gfx };
+        Assert.False(GfxObjDegradeResolver.IsRuntimeHiddenMarker(
+            id => gfxObjs.GetValueOrDefault(id), _ => null, baseId));
+    }
+
+    /// <summary>slot 0 is editor-only (MaxDist=0) but degrades to a REAL mesh (no id-0
+    /// entry) — a genuine close-only LOD, not an invisible marker. Do NOT skip.</summary>
+    [Fact]
+    public void IsRuntimeHiddenMarker_EditorSlotButDegradesToRealMesh_False()
+    {
+        const uint baseId = 0x01002000u;
+        const uint degradeId = 0x11002000u;
+        var gfx = new GfxObj { Flags = GfxObjFlags.HasDIDDegrade, DIDDegrade = degradeId };
+        var info = new GfxObjDegradeInfo
+        {
+            Degrades =
+            {
+                new GfxObjInfo { Id = baseId, MaxDist = 0f },
+                new GfxObjInfo { Id = 0x01002001u, MaxDist = float.MaxValue },
+            },
+        };
+        var gfxObjs = new Dictionary<uint, GfxObj> { [baseId] = gfx };
+        var infos = new Dictionary<uint, GfxObjDegradeInfo> { [degradeId] = info };
+
+        Assert.False(GfxObjDegradeResolver.IsRuntimeHiddenMarker(
+            id => gfxObjs.GetValueOrDefault(id), id => infos.GetValueOrDefault(id), baseId));
+    }
 }