Text (ET+errata): Each player returns each creature card in his or her graveyard to the battlefield with an additional -1/-1 counter on it. [Oracle 2009/07/08]
Creatures that enter play with zero or less toughness because of the -1/-1 counters are put back into the graveyard as a state-based effect before any player can play any spells or abilities. [Eventide FAQ 2008/07/08]
