At the beggining of your upkeep, if you control an island, put a +1/+1 counter on Pond Wyrmling, If you don't control an island, sacrifice Pond Wyrmling instead.

Whenever Thurdrold, The Many Masks enters the battlefield or attacks, You may pay {b}{b}, if you do, Thurdrold, The Many Masks becomes a copy of target nonlegendary creature you control until end of turn.