diff --git a/src/data/ability.ts b/src/data/ability.ts
index cad625715..fa5f8ec75 100644
--- a/src/data/ability.ts
+++ b/src/data/ability.ts
@@ -2347,6 +2347,26 @@ export class PostFaintContactDamageAbAttr extends PostFaintAbAttr {
   }
 }
 
+/** 
+ * Attribute used for abilities (Innards Out) that damage the opponent based on how much HP the last attack used to knock out the owner of the ability.
+ */
+export class PostFaintHPDamageAbAttr extends PostFaintAbAttr {
+  constructor() {
+    super ();
+  }
+
+  applyPostFaint(pokemon: Pokemon, passive: boolean, attacker: Pokemon, move: PokemonMove, hitResult: HitResult, args: any[]): boolean {
+    const damage = pokemon.turnData.attacksReceived[0].damage;
+    attacker.damageAndUpdate((damage), HitResult.OTHER);
+    attacker.turnData.damageTaken += damage;
+    return true;
+  } 
+
+  getTriggerMessage(pokemon: Pokemon, abilityName: string, ...args: any[]): string {
+    return getPokemonMessage(pokemon, `'s ${abilityName} hurt\nits attacker!`);
+  }
+}
+
 export class RedirectMoveAbAttr extends AbAttr {
   apply(pokemon: Pokemon, passive: boolean, cancelled: Utils.BooleanHolder, args: any[]): boolean {
     if (this.canRedirect(args[0] as Moves)) {
@@ -3398,7 +3418,8 @@ export function initAbilities() {
       .attr(FieldPriorityMoveImmunityAbAttr)
       .ignorable(),
     new Ability(Abilities.INNARDS_OUT, 7)
-      .unimplemented(),
+      .attr(PostFaintHPDamageAbAttr)
+      .bypassFaint(),
     new Ability(Abilities.DANCER, 7)
       .unimplemented(),
     new Ability(Abilities.BATTERY, 7)