Giant Shark 

Creature — Shark
This creature can't attack unless defending player controls an Island. Whenever this creature blocks or becomes blocked by a creature that has been dealt damage this turn, this creature gets +2/+0 and gains trample until end of turn. When you control no Islands, sacrifice this creature.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyLEGALvintageLEGALcommanderLEGAL