Sealock Monster (42) [Duel Decks: Elspeth vs. Kiora]

This creature can't attack unless defending player controls an Island. {5}{U}{U}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.) When this creature becomes monstrous, target land becomes an Island in addition to its other types.