The Necrolance

The Necrolance enters the battlefield with three +1/+1 counters on it.
Whenever another creature you control dies, if it had a +1/+1 counter on it, put a +1/+1 counter on the Necrolance.
When the Necrolance dies, create an X/X black and green Hydra creature token, where X is the number of +1/+1 counters on the Necrolance.