Hadean Hydra

Hadean Hydra has power and toughness equal to the number of +1/+1 counters on it.
Whenever Hadean Hydra dies, return it to the battlefield under it's owner's control with X +1/+1 counters on it, where X is one plus the number of +1/+1 it had on it when it died.
The underworld cannot hold it, for there is where it began.