Dryad of the Great Oak

Bestow {1}{g}{g} (This card is an aura until removed.)
Enchanted creature gets +0/+4.
When Dryad is cast or detached, enchanted creature or Dryad gains:
Constellation - Untap this creature.
Vigor (This creature's toughness is refreshed each phase.)
{t}: Add {g} or untap target creature.
If Dryad detaches to become a creature, pay {1}{g}{g} or return it to your hand.