Release the Horde

At the beginning of combat on your turn, you may put a 2/2 Zombie creature token onto the battlefield tapped and attacking.
Whenever a Zombie creature you control dies, you may pay {u/b}{u/r}. If you do, return it to the battlefield from your graveyard tapped at the beginning of your next upkeep.
I believe, given enough time, I can devise an efficient way to bring back our departed