Zovod, Dreaded Summoner

Zovod, Dreaded Summoner enters the battlefield with 5 summon counters on it.
Whenever you cast a spell, you may remove a summon counter from Zovod, Dreaded Summoner. Then if there are no summon counters on Zovod, Dreaded Summoner, exile it. Then return all creature cards from you graveyard to the battlefield.