diff --git a/PKHeX.Core/Legality/Encounters/Templates/Gen6/EncounterSlot6AO.cs b/PKHeX.Core/Legality/Encounters/Templates/Gen6/EncounterSlot6AO.cs
index 320ef92c0..0c863964e 100644
--- a/PKHeX.Core/Legality/Encounters/Templates/Gen6/EncounterSlot6AO.cs
+++ b/PKHeX.Core/Legality/Encounters/Templates/Gen6/EncounterSlot6AO.cs
@@ -127,7 +127,14 @@ public sealed record EncounterSlot6AO(EncounterArea6AO Parent, ushort Species, b
             return false;
 
         if (evo.Form != Form && !IsRandomUnspecificForm)
-            return false;
+        {
+            if (Species is not ((ushort)Core.Species.Deerling or (ushort)Core.Species.Sawsbuck))
+                return false;
+
+            // Deerling can change between forms if imported to a future Gen8+ game.
+            if (pk.Format < 8 || evo.Form >= 4)
+                return false;
+        }
 
         return true;
     }
diff --git a/PKHeX.Core/Legality/Encounters/Templates/Gen9/EncounterSlot9.cs b/PKHeX.Core/Legality/Encounters/Templates/Gen9/EncounterSlot9.cs
index ebc974a4b..c3a053a85 100644
--- a/PKHeX.Core/Legality/Encounters/Templates/Gen9/EncounterSlot9.cs
+++ b/PKHeX.Core/Legality/Encounters/Templates/Gen9/EncounterSlot9.cs
@@ -238,7 +238,17 @@ public sealed record EncounterSlot9(EncounterArea9 Parent, ushort Species, byte
             if (m.RibbonMarkDawn && !CanSpawnAtTime(RibbonIndex.MarkDawn))
                 return EncounterMatchRating.DeferredErrors;
         }
+
+        if (IsFormArgDeferralRelevant(pk.Species) && pk is IFormArgument f)
+        {
+            bool isFormArg0 = f.FormArgument == 0;
+            bool mustBeZero = IsFormArgDeferralRelevant(Species);
+            if (isFormArg0 != mustBeZero)
+                return EncounterMatchRating.DeferredErrors;
+        }
         return EncounterMatchRating.Match;
+
+        static bool IsFormArgDeferralRelevant(ushort species) => species is (ushort)Core.Species.Kingambit or (ushort)Core.Species.Annihilape;
     }
     #endregion
 }
diff --git a/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/0585-01 ★ - Deerling - 11D0C90A7F2F pk6 formchange.pk9 b/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/0585-01 ★ - Deerling - 11D0C90A7F2F pk6 formchange.pk9
new file mode 100644
index 000000000..7944c585a
Binary files /dev/null and b/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/0585-01 ★ - Deerling - 11D0C90A7F2F pk6 formchange.pk9 differ
diff --git a/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/FormArg/0979 - Second Wind - F595DB8A1056.pk9 b/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/FormArg/0979 - Second Wind - F595DB8A1056.pk9
new file mode 100644
index 000000000..dd7f47cc1
Binary files /dev/null and b/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/FormArg/0979 - Second Wind - F595DB8A1056.pk9 differ
diff --git a/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/FormArg/0983 - Kingambit - 6BE42E9A9EF4 0 asKing.pk9 b/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/FormArg/0983 - Kingambit - 6BE42E9A9EF4 0 asKing.pk9
new file mode 100644
index 000000000..f47ccf53b
Binary files /dev/null and b/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/FormArg/0983 - Kingambit - 6BE42E9A9EF4 0 asKing.pk9 differ
diff --git a/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/FormArg/0983 - Kingambit - 6BE72E9A9EF4 3 asBisharp.pk9 b/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/FormArg/0983 - Kingambit - 6BE72E9A9EF4 3 asBisharp.pk9
new file mode 100644
index 000000000..a015b8df5
Binary files /dev/null and b/Tests/PKHeX.Core.Tests/Legality/Legal/Generation 9/FormArg/0983 - Kingambit - 6BE72E9A9EF4 3 asBisharp.pk9 differ