Mikaeus, the Unhallowed | Magic: The Gathering
Formats Mikaeus, the Unhallowed is Legal in
Official Oracle Text for Mikaeus, the Unhallowed
Whenever a Human deals damage to you, destroy it.
Other non-Human creatures you control get +1/+1 and have undying. (When a creature with undying dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)
Official Rulings for Mikaeus, the Unhallowed
1/22/2011 : The +1/+1 bonus that Mikaeus gives to other non-Human creatures is not a counter and won't prevent the undying ability from working.
1/22/2011 : Mikaeus, the Unhallowed and the Innistrad set's Mikaeus, the Lunarch can be on the battlefield at the same time. The "legend rule" applies only to legendary permanents that have exactly the same name.