Nexxis, Phyrexian Evolutionist

Defender
Graft 1 (This creature enters the battlefield with a +1/+1 counter on it. Whenever another creature enters the battlefield, you may move a +1/+1 counter from this creature onto it.)
Undying (When this creature 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.)