Marshfly, Bridge to Destiny

Marshfly, Bridge to Destiny enters the battlfield tapped.
{t}: Add {u} or {g} to your mana pool. Spend this mana only to cast Creature spells. If a legendary creature spell is cast using mana produced by this land this way, put a +1/+1 counter on it.
{g/u}, {t}: Put a +1/+1 counter on target creature. If that creature is legendary, you may draw a card.