The Ancient Three

The Ancient Three enters the battlefield with
X +1/+1 counters on it, where X is the amount
of mana spent to cast it. Whenever a Merfolk
enters the battlefield under your control, put a
+1/+1 counter on The Ancient Three.
Remove X +1/+1 counters from The Ancient
Three: Put X +1/+1 counters on each Merfolk
you control. Merfolk you control gain Islandwalk
and Forestwalk until end of turn.