Methuselah, the Prime

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.)
Undying Persistence (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. This removes the +1/+1 counter from Undying, instead of giving a -1/-1 counter.)