Hallo, the Spirit of Tricks

If this card is Normal or Special Summoned: You can activate this effect; if you still control this face-up card, your opponent chooses 1 of these effects for you to apply.• This card gains 800 ATK for each Fiend monster currently in your GY.• Inflict 500 damage to your opponent for each Fiend monster in your GY.If this card is destroyed by battle or card effect: You can send 1 monster your opponent controls to the GY.You can only use each effect of "Hallo, the Spirit of Tricks" once per turn.