You can Ritual Summon this card with any "Vendread" Ritual Spell. Once per battle, if this card battles an opponent's monster, during damage calculation (Quick Effect): You can banish 1 Zombie monster from your GY; this card gains 300 ATK. If this Ritual Summoned card is sent to the GY: You can add 1 Ritual Spell from your Deck to your hand, and if you do, send 1 "Vendread" monster from your Deck to the GY. You can only use this effect of "Revendread Slayer" once per turn.