Demigod of the Tistina (Quarter Century Secret Rare)

If you control a "Tistina" card: You can Special Summon this card from your hand, then you can add 1 "Tistina" Spell/Trap from your Deck to your hand. During your opponent's turn, if you control "Crystal God Tistina" (Quick Effect): You can change as many monsters your opponent controls as possible to face-down Defense Position, then you can send all face-up cards your opponent controls to the GY. You can only use each effect of "Demigod of the Tistina" once per turn.