Depthwood Hydra

Whenever you take combat damage, put a +1/+1 counter on Depthwood Hydra. Then, if there are 5 or more +1/+1 counters on Depthwood Hydra, Depthwood Hydra deals 2 damage to it's controller.
{t}: Remove two +1/+1 counters from Depthwood Hydra.
Whenever it's master is hurt, it get's stronger, until it overpowers it's master.