Malachite, Ocean Terror

Gem Fusion(When this enters, sacrifice it unless you
exile two other Gems without Gem Fusion you control
until it leaves the battlefield. Put a +1/+1 counter on
it for each color it shares with those Gems.)

At the beginning of combat on your turn, untap up
to X Islands you control, where X is half of
Malachite's power, rounded down. Those islands
become X/X blue Elemental creatures with trample
and haste in addition to their other colors and types
until end of turn.