The Heron Moon
Legendary Land$0.30
: Add . , : Exile the bottom card of target opponent's library. Whenever one or more cards an opponent owns are put into exile, put a release counter on The Heron Moon. Then if it has thirteen or more release counters on it, sacrifice it and create a copy of Emrakul, the Promised End. Cast it without paying its mana cost.
colorlessNot legal in Commander