Guilt of the Sinful Spoils (ROTA-EN074 Common)

If your opponent Special Summons a monster(s) from the Deck or Extra Deck and you control a "Diabellstar" Monster Card (except during the Damage Step): Target 1 monster your opponent controls; shuffle it into the Deck. During the Damage Step, when your "Diabellstar" monster battles an opponent's monster: You can banish this card from your GY; that opponent's monster's ATK becomes halved until the end of this turn. You can only use each effect of "Guilt of the Sinful Spoils" once per turn.
Common
Trap
From the Yu-Gi-Oh set Rage of the Abyss