Athenix, Titan of Depths

{u}{u}: Submerge a creature, then submerge
a creature your opponents control. (Only
creatures with reach or that are submerged
can target or block submerged creatures)
Reach
At the beginning of your combat step, tap
all islands in play and add {u} for each of
them. Mana does not empty from your mana pool until the end of turn.