If your "Performapal" monster attacked, after damage calculation: You can target 1 face-up monster your opponent controls; that target loses ATK equal to the ATK of that "Performapal" monster.
[Pendulum Effect]
Once per turn, at the start of the Damage Step, when your "Performapal" monster battles an opponent's face-up monster: You can make that opponent's monster lose 600 ATK (even if this card leaves the field).