Khaimero, Maws of Chaos

Khaimero, Maws of Chaos, enters the battlefield
with X +1/+1 counters on it.
Hydras you control enter the battlefield with X
+1/+1 counters on them, where X is Khaimero's
power.
Whenever Khaimero attacks, you may sacrifice a
land. If you do, put 3 +1/+1 counters on
Khaimero.