This card's activation and effect cannot be negated. If you control a monster whose original name is "Slifer the Sky Dragon": Destroy as many face-up monsters your opponent controls as possible, then, if you activated this card during your Main Phase, you can apply the following effect.
• Draw cards equal to the number of monsters destroyed by this effect and sent to your opponent's GY, also you can only attack with 1 monster this turn.
You can only activate 1 "Thunderforce Attack" per turn.