Hidden Roots Bog

{t}: Add {g} or {b} to your manapool
{2}{b/g}{t}: Create either a 1/1 green saporling creature token with forestwalk, or a 1/1 black rat creature token with swampwalk, put it onto the battlefield.
{4}{b/g}{t}: Sacrifice 5 creatures, create a 7/9 black and green Legendary Elemental Creature token with swampwalk, forestwalk, hexproof, and trample. Exile Hidden Roots Bog