Regenerator

Regenerator enters the battlefield with five +1/+1 counters on it.
If damage would be dealt to Regenerator while it
has a +1/+1 counter on it, prevent that damage
and remove that many +1/+1 counters from it.
At the beginning of your upkeep, if Regenerator
has less than five +1/+1 counters on it, add one
+1/+1 counter to Regenerator.