Trample

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Shroud (This creature can't be the target of spells or abilities.)

Trample

Leviathan enters the battlefield tapped and doesn't untap during your untap step.

At the beginning of your upkeep, you may sacrifice two Islands. If you do, untap Leviathan.

Leviathan can't attack unless you sacrifice two Islands. (This cost is paid as attackers are declared.)

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

All lands are Islands in addition to their other types.

Creatures without flying or islandwalk can't attack.