More abilities, refactor stealing held items

Plugins/PkmnLib.Plugin.Gen7/Scripts/Abilities/StanceChange.cs

@@ -0,0 +1,30 @@
+using PkmnLib.Static.Moves;
+
+namespace PkmnLib.Plugin.Gen7.Scripts.Abilities;
+
+/// <summary>
+/// Stance Change is an ability that changes Aegislash's form depending on the move used.
+///
+/// <see href="https://bulbapedia.bulbagarden.net/wiki/Stance_Change_(Ability)">Bulbapedia - Stance Change</see>
+/// </summary>
+[Script(ScriptCategory.Ability, "stance_change")]
+public class StanceChange : Script
+{
+    /// <inheritdoc />
+    public override void OnBeforeMove(IExecutingMove move)
+    {
+        if (move.User.Species.Name != "aegislash")
+            return;
+
+        if (move.UseMove.Category is not (MoveCategory.Physical or MoveCategory.Special) ||
+            move.User.Form.Name == "blade" || !move.User.Species.TryGetForm("blade", out var bladeForm))
+            return;
+        EventBatchId batchId = new();
+        move.Battle.EventHook.Invoke(new AbilityTriggerEvent(move.User)
+        {
+            BatchId = batchId,
+        });
+        move.User.ChangeForm(bladeForm, batchId);
+        // Kings shield is handled in the move script.
+    }
+}