Malachite, Ocean Terror

Gem Fusion (As this creature enters, put two Gems
you control that share a color with it under it. They
combine into the creature on top plus all abilities from
under it.)

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.