Purgatory Sorcery, Blood Oath Formation

■ You may only cast this card if you have a card with "Purgatory Knights" in its card name on your field.

■ Draw a card, and for this turn, all cards with "Purgatory Knights" in their card names on your field cannot be destroyed, nor returned to hand, by your opponent's card effects. You may only cast "Purgatory Sorcery, Blood Oath Formation" once per turn.