Satoru Umezawa

Whenever you activate a ninjutsu ability, look at the top three cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order. This ability triggers only once each turn.
Each creature card in your hand has ninjutsu {2}{U}{B}.

Leviathan

Trample
Leviathan enters 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.)

Polar Kraken

Trample
Polar Kraken enters tapped.
Cumulative upkeep—Sacrifice a land. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)

Thing from the Deep

Whenever Thing from the Deep attacks, sacrifice it unless you sacrifice an Island.

Marjhan

Marjhan doesn't untap during your untap step.
{U}{U}, Sacrifice a creature: Untap Marjhan. Activate only during your upkeep.
Marjhan can't attack unless defending player controls an Island.
{U}{U}: Marjhan gets -1/-0 until end of turn and deals 1 damage to target attacking creature without flying.
When you control no Islands, sacrifice Marjhan.

Dancing Scimitar

Flying (This creature can't be blocked except by creatures with flying or reach.)