Harbor Serpent 
Creature — Serpent
Islandwalk (This creature can't be blocked as long as defending player controls an Island.) This creature can't attack unless there are five or more Islands on the battlefield.
Legality
standardNOT LEGALpioneerNOT LEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL