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.