Unbreathing Horde enters the battlefield with a +1/+1 counter on it for each other Zombie you control and each Zombie card in your graveyard.
If Unbreathing Horde would be dealt damage, prevent that damage and remove a +1/+1 counter from it.
9/22/2011 Only one +1/+1 counter will be removed, no matter how much damage is prevented.
9/22/2011 If Unbreathing Horde has no +1/+1 counters on it (but its toughness is raised above 0 by another effect), any damage dealt to it will still be prevented, even though no counter will be removed.
9/22/2011 If Unbreathing Horde enters the battlefield from a graveyard, it will count itself when determining how many +1/+1 counters it enters the battlefield with.