Add smeargle verifier branch

Add gen2 nosketch moves while we're here, and Stadium2's extra quirk one.

PKHeX.Core/Legality/LearnSource/Group/LearnGroup2.cs

@@ -44,6 +44,9 @@ public sealed class LearnGroup2 : ILearnGroup
 
         // Uh-oh, not all moves are verified yet.
         // To visit Gen1, we need to invalidate moves that can't be learned in Gen1 or re-learned in Gen2.
+        if (GetPrevious(pk, history, enc, option) is null)
+            return true; // can't even visit, don't bother purging.
+
         for (int i = 0; i < result.Length; i++)
         {
             if (current[i] <= Legal.MaxMoveID_1)

PKHeX.Core/Legality/LearnSource/LearnEnvironment.cs

@@ -31,7 +31,7 @@ public static class LearnEnvironmentExtensions
     public static byte GetGeneration(this LearnEnvironment value) => value switch
     {
         RB or YW => 1,
-        GS or C => 2,
+        GS or C or Stadium2 => 2,
         RS or E or FR or LG => 3,
         DP or Pt or HGSS => 4,
         BW or B2W2 => 5,
@@ -45,7 +45,7 @@ public static class LearnEnvironmentExtensions
     public static ReadOnlySpan<EvoCriteria> GetEvolutions(this LearnEnvironment value, EvolutionHistory history) => value switch
     {
         RB or YW => history.Gen1,
-        GS or C => history.Gen2,
+        GS or C or Stadium2 => history.Gen2,
         RS or E or FR or LG => history.Gen3,
         DP or Pt or HGSS => history.Gen4,
         BW or B2W2 => history.Gen5,

PKHeX.Core/Legality/Learnset/LearnsetStadium.cs

@@ -84,8 +84,8 @@ public bool Validate(ReadOnlySpan<ushort> moves, byte level, Span<bool> flag)
     {
         bool anyInvalid = false;
 
-        // todo: is stadium smart to disallow egg moves+event, or multiple event moves (pikachu)?
-        // Naive checker only checking individual moves in isolation.
+        // Stadium2 is not smart enough to disallow egg moves+event, or multiple event moves (Pikachu).
+        // Naive checker only checks if all individual moves are in its list with sufficient level.
         for (int i = 0; i < moves.Length; i++)
         {
             var move = moves[i];
@@ -100,6 +100,19 @@ public bool Validate(ReadOnlySpan<ushort> moves, byte level, Span<bool> flag)
         return !anyInvalid;
     }
 
+    public static bool ValidateSmeargle(ReadOnlySpan<ushort> moves, Span<bool> flag)
+    {
+        bool anyInvalid = false;
+        for (int i = 0; i < moves.Length; i++)
+            anyInvalid |= flag[i] = !IsSketchValid(moves[i]);
+        return !anyInvalid;
+    }
+
+    /// <summary>
+    /// All others are covered by Mainline possibility. Baton Pass is the only error.
+    /// </summary>
+    public static bool IsSketchValid(ushort move) => move is not (ushort)Move.BatonPass;
+
     /// <summary>
     /// Converts a <see cref="BinLinkerAccessor"/> into an array of <see cref="LearnsetStadium"/>.
     /// </summary>

PKHeX.Core/Legality/Verifiers/MiscVerifier.cs

@@ -176,9 +176,17 @@ private void VerifyIsMovesetAllowed(LegalityAnalysis data, SK2 sk2)
         sk2.GetMoves(moves);
         Span<bool> flags = stackalloc bool[4];
 
-        var learn = LearnSource2Stadium.Instance.GetLearnsetStadium(sk2.Species, sk2.Form);
-        if (learn.Validate(moves, sk2.CurrentLevel, flags))
-            return;
+        if (sk2.Species is (ushort)Species.Smeargle)
+        {
+            if (LearnsetStadium.ValidateSmeargle(moves, flags))
+                return;
+        }
+        else
+        {
+            var learn = LearnSource2Stadium.Instance.GetLearnsetStadium(sk2.Species, sk2.Form);
+            if (learn.Validate(moves, sk2.CurrentLevel, flags))
+                return;
+        }
 
         var parse = data.Info.Moves;
         for (int i = 0; i < flags.Length; i++)

PKHeX.Core/Moves/MoveInfo.cs

@@ -183,6 +183,7 @@ public static bool IsSketchValid(ushort move, EntityContext context)
     /// <param name="context">Context currently present in</param>
     private static bool IsSketchPossible(ushort move, EntityContext context) => context switch
     {
+        Gen2 when move is (int)SelfDestruct or (int)Explosion or (ushort)Mimic or (ushort)Metronome or (ushort)MirrorMove or (ushort)Transform or (ushort)SleepTalk => false,
         Gen6 when move is (int)ThousandArrows or (int)ThousandWaves or (int)LightofRuin => false,
         Gen7 when move is (int)LightofRuin => false,
         Gen8b when IsDummiedMove(MoveInfo8b.DummiedMoves, move) => false,