First couple abilities implemented

PkmnLib.Dynamic/BattleFlow/MoveTurnExecutor.cs

@@ -263,6 +263,8 @@ public static class MoveTurnExecutor
                                 }
                             }
                         }
+                        if (target.IsFainted)
+                            executingMove.RunScriptHook(x => x.OnOpponentFaints(executingMove, target, hitIndex));
                     }
                 }
             }

PkmnLib.Dynamic/Events/AbilityTriggerEvent.cs

@@ -0,0 +1,20 @@
+using PkmnLib.Dynamic.Models;
+using PkmnLib.Static.Species;
+using PkmnLib.Static.Utils;
+
+namespace PkmnLib.Dynamic.Events;
+
+public record AbilityTriggerEvent : IEventData
+{
+    public IPokemon Pokemon { get; }
+    public IAbility? Ability { get; }
+
+    public AbilityTriggerEvent(IPokemon pokemon)
+    {
+        Pokemon = pokemon;
+        Ability = pokemon.ActiveAbility;
+    }
+
+    /// <inheritdoc />
+    public EventBatchId BatchId { get; init; }
+}

PkmnLib.Dynamic/Libraries/DataLoaders/AbilityDataLoader.cs

@@ -59,7 +59,7 @@ public static class AbilityDataLoader
 
         var flags = serialized.Flags.Select(x => new StringKey(x)).ToImmutableHashSet();
 
-        var ability = new AbilityImpl(name, effectName, parameters, flags);
+        var ability = new AbilityImpl(name, effectName, parameters, flags, serialized.CanBeChanged ?? true);
         return ability;
     }
 }

PkmnLib.Dynamic/Libraries/DataLoaders/Models/SerializedAbility.cs

@@ -19,4 +19,6 @@ public class SerializedAbility
     /// A collection of arbitrary flags that can be used to mark the ability with specific properties.
     /// </summary>
     public string[] Flags { get; set; } = [];
+
+    public bool? CanBeChanged { get; set; }
 }

PkmnLib.Dynamic/Models/BattleSide.cs

@@ -271,18 +271,25 @@ public class BattleSideImpl : ScriptSource, IBattleSide
             pokemon.SetBattleData(Battle, Index);
             pokemon.SetOnBattlefield(true);
             pokemon.SetBattleSidePosition(position);
+            Battle.EventHook.Invoke(new SwitchEvent(Index, position, pokemon));
+            pokemon.RunScriptHook(script => script.OnSwitchIn(pokemon, position));
+
             foreach (var side in Battle.Sides)
             {
                 if (side == this)
                     continue;
+                var scripts = new List<IEnumerable<ScriptContainer>>(10);
                 foreach (var opponent in side.Pokemon.WhereNotNull())
                 {
                     opponent.MarkOpponentAsSeen(pokemon);
                     pokemon.MarkOpponentAsSeen(opponent);
+
+                    scripts.Clear();
+                    opponent.GetOwnScripts(scripts);
+                    opponent.RunScriptHook(script => script.OnOpponentSwitchIn(pokemon, position));
                 }
+                side.RunScriptHook(script => script.OnOpponentSwitchIn(pokemon, position));
             }
-            Battle.EventHook.Invoke(new SwitchEvent(Index, position, pokemon));
-            pokemon.RunScriptHook(script => script.OnSwitchIn(pokemon, position));
         }
         else
         {

PkmnLib.Dynamic/Models/ExecutingMove.cs

@@ -46,6 +46,16 @@ public interface IHitData
     /// Fails the hit.
     /// </summary>
     void Fail();
+
+    /// <summary>
+    /// Sets a flag on the hit data. This is used to mark certain conditions or states
+    /// </summary>
+    void SetFlag(StringKey flag);
+
+    /// <summary>
+    /// Checks whether a flag is set on the hit data.
+    /// </summary>
+    bool HasFlag(StringKey flag);
 }
 
 /// <inheritdoc />
@@ -71,6 +81,18 @@ public record HitData : IHitData
 
     /// <inheritdoc />
     public void Fail() => HasFailed = true;
+
+    private HashSet<StringKey>? _flags;
+
+    /// <inheritdoc />
+    public void SetFlag(StringKey flag)
+    {
+        _flags ??= [];
+        _flags.Add(flag);
+    }
+
+    /// <inheritdoc />
+    public bool HasFlag(StringKey flag) => _flags != null && _flags.Contains(flag);
 }
 
 /// <summary>

PkmnLib.Dynamic/Models/Pokemon.cs

@@ -401,7 +401,7 @@ public interface IPokemon : IScriptSource, IDeepCloneable
     /// <summary>
     /// Changes the ability of the Pokémon.
     /// </summary>
-    void ChangeAbility(IAbility ability);
+    bool ChangeAbility(IAbility ability);
 
     /// <summary>
     /// Whether the Pokémon is levitating. This is used for moves like Magnet Rise, and abilities such as
@@ -1197,8 +1197,10 @@ public class PokemonImpl : ScriptSource, IPokemon
     }
 
     /// <inheritdoc />
-    public void ChangeAbility(IAbility ability)
+    public bool ChangeAbility(IAbility ability)
     {
+        if (!ability.CanBeChanged)
+            return false;
         OverrideAbility = ability;
         if (Library.ScriptResolver.TryResolve(ScriptCategory.Ability, ability.Name, ability.Parameters,
                 out var abilityScript))
@@ -1210,6 +1212,7 @@ public class PokemonImpl : ScriptSource, IPokemon
         {
             AbilityScript.Clear();
         }
+        return true;
     }
 
     /// <inheritdoc />

PkmnLib.Dynamic/ScriptHandling/Script.cs

@@ -546,6 +546,13 @@ public abstract class Script : IDeepCloneable
     {
     }
 
+    /// <summary>
+    /// This function is triggered on a Pokemon and its parents when an opponent switches in.
+    /// </summary>
+    public virtual void OnOpponentSwitchIn(IPokemon pokemon, byte position)
+    {
+    }
+
     /// <summary>
     /// This function is triggered on a Pokemon and its parents when the given Pokemon consumes the
     /// held item it had.

PkmnLib.Dynamic/ScriptHandling/ScriptResolver.cs

@@ -34,10 +34,7 @@ public class ScriptResolver
         }
 
         script = scriptCtor();
-        if (parameters != null)
-        {
-            script.OnInitialize(parameters);
-        }
+        script.OnInitialize(parameters);
 
         return true;
     }