From 478413e8cd456b705ca1b176cc0d93d7227cd9e5 Mon Sep 17 00:00:00 2001
From: Kurt <kaphotics@gmail.com>
Date: Sun, 9 Jul 2023 20:22:01 -0700
Subject: [PATCH] Discard Fairy type Arceus when reversing

https://projectpokemon.org/home/forums/topic/63635-pkhex-230709-bugs/
---
 .../Evolutions/EvolutionGroup/EvolutionGroup6.cs         | 9 ++++++++-
 PKHeX.Core/Legality/Verifiers/NicknameVerifier.cs        | 2 +-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/PKHeX.Core/Legality/Evolutions/EvolutionGroup/EvolutionGroup6.cs b/PKHeX.Core/Legality/Evolutions/EvolutionGroup/EvolutionGroup6.cs
index 1588d6bce..fea06ff16 100644
--- a/PKHeX.Core/Legality/Evolutions/EvolutionGroup/EvolutionGroup6.cs
+++ b/PKHeX.Core/Legality/Evolutions/EvolutionGroup/EvolutionGroup6.cs
@@ -18,7 +18,8 @@ public int Devolve(Span<EvoCriteria> result, PKM pk, EvolutionOrigin enc)
         int present = 1;
         for (int i = 1; i < result.Length; i++)
         {
-            var prev = result[i - 1];
+            ref var prev = ref result[i - 1];
+            RevertMutatedForms(ref prev);
             if (!TryDevolve(prev, pk, prev.LevelMax, enc.LevelMin, enc.SkipChecks, out var evo))
                 continue;
 
@@ -30,6 +31,12 @@ public int Devolve(Span<EvoCriteria> result, PKM pk, EvolutionOrigin enc)
         return present;
     }
 
+    private static void RevertMutatedForms(ref EvoCriteria evo)
+    {
+        if (evo is { Species: (ushort)Species.Arceus, Form: 17 }) // Fairy, prevent it hitting Gen5 (as Fairy does not exist yet).
+            evo = evo with { Form = 0 }; // Normal
+    }
+
     public bool TryDevolve(ISpeciesForm head, PKM pk, byte currentMaxLevel, byte levelMin, bool skipChecks, out EvoCriteria result)
     {
         return Tree.Reverse.TryDevolve(head, pk, currentMaxLevel, levelMin, skipChecks, out result);
diff --git a/PKHeX.Core/Legality/Verifiers/NicknameVerifier.cs b/PKHeX.Core/Legality/Verifiers/NicknameVerifier.cs
index 2372d3d03..4bde7510b 100644
--- a/PKHeX.Core/Legality/Verifiers/NicknameVerifier.cs
+++ b/PKHeX.Core/Legality/Verifiers/NicknameVerifier.cs
@@ -413,7 +413,7 @@ private static void VerifyTrade8b(LegalityAnalysis data, EncounterTrade8b t)
                 data.AddLine(GetInvalid(string.Format(LOTLanguage, $"{Japanese}/{German}", $"{(LanguageID)pk.Language}"), CheckIdentifier.Language));
         }
 
-        if (t.Species == (int)Species.Chatot && pk.Language == (int)French)
+        if (t.Species == (int)Species.Chatot && pk is { Language: (int)French, IsNicknamed: false })
         {
             // NgWord disallows the French nickname (Pijouk) and resets it back to default (Pijako).
             // Let it be anything (Nicknamed or not) and just verify the OT.