Brainstealer Dragon 5BB
Creature — Dragon Horror
Flying

At the beginning of your end step, exile the top card of each opponent s library. You may play those cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.

Whenever a nonland permanent an opponent owns enters the battlefield under your control, they lose life equal to its mana value.