Experimental Hydra

Graft X (This creature enters the battlefield with X +1/+1 counters on it. Whenever another creature enters the battlefield, you may move a +1/+1 counter from this creature onto it.)
When Experimental Hydra dies, each creature with a +1/+1 counter on it gets +1/+1 counters equal to the number of creatures you control with +1/+1 counters.