At the beginning of your end step, you may put target creature card from an opponent's graveyard onto the battlefield under your control. When a creature put onto the battlefield with this scheme dies, abandon this scheme.
My Undead Horde Awakens is not legal in any format.
Rulings
2010-06-15
When this scheme is abandoned, nothing happens to the rest of the creatures that were put onto the battlefield with it. They simply remain on the battlefield.
2010-06-15
You put a creature card on the battlefield this way during the end step of each of your turns. As soon as any one of those creatures is put back into a graveyard for any reason, this scheme is abandoned.