Vraelyn, Chaos Incarnate

Each time an opponent casts a spell, they exile it, then reveal cards from the top of their library until they reveal a spell with a lesser converted mana cost. They must cast the revealed card, and if they do, they may cast it without paying its mana cost. It gains flash.
Whenever a player casts a spell, if there are other spells below it on the stack, counter those spells.
"I have glimpsed the unthinkable. You cannot think.