Dryad of the Melting Wilds

When Dryad of the Melting Wilds enters
the battlefield, for each untapped land you
control, add one mana of any color. Until
end of turn, this mana doesn't empty from
your mana pool as steps and phases end.
Evoke {3} (You may cast this spell for its evoke
cost. If you do, it's sacrificed when it enters the
battlefield.)