Vain Betrayer (JOTL-EN073) [Judgment of the Light]

When an opponent's Xyz Monster declares an attack: Activate this card by targeting the attacking monster. It cannot attack, also its effects are negated. While that monster is on the field, during each of your opponent's End Phases: Send the top 3 cards of your opponent's Deck to the Graveyard. When that monster leaves the field, destroy this card.