Emrakul, World Desolator

Flying, indestructible, hexproof
Annihilator 6 (Whenever this creature attacks, defending played sacrifices six permanents.)
Madness {6}: (Exile, and put three time counters on Emrakul, World Desolator. At the beginning of your upkeep, remove a time counters. When there are no time counters left on Emrakul, World Desolator, you may cast it from exile for its madness cost. Only activate this ability once per game.)