When an opponent's monster declares a direct attack: You can Special Summon 1 "Graydle" monster from your Deck in Attack Position, if you control no monsters. When a "Graydle" monster you control declares a direct attack: You can target 1 monster in your opponent's Graveyard; Special Summon that target to their side of the field, if they control no monsters. You can only use each effect of "Graydle Parasite" once per turn.
