Deathless Boa

Deathtouch, Persist(When this permanent is put into a graveyard from the battlefield, 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.)
Immunity {1}{b/g} ({1}{b/g}: Remove a -1/-1 counter from this creature.)
All damage dealt to Deathless Boa is dealt in the form of -1/-1 counters.