Doomsday Clock

Each time an opponent casts a spell, put a Clock counter on Doomsday Clock.
At the end of your turn, if there is exactly
12 Clock counters on it, sacrifice
Doomsday Clock, then randomly destroy 12 permanents on the battlefield, exile 12 cards
randomly from all graveyards, and randomly mill
12 cards from any library.
{2},{t}: Remove a Clock counter from Doomsday
Clock.