Doomsilver Kraken

When Doomsilver Kraken enters the battlefield,
exile it under an island you control.
For as long as Doomsilver Kraken remains exiled,
chosen island gains: "You may
choose not to untap this island during your untap
step." When chosen land untaps,
exile it. Return Moonsilver Kraken from exile to
the battlefield. It enters the
battlefield tapped and attacking.
Trample