Fenbriar Fortress

Fenbriar Fortress enters the battlefield tapped.
{t}: Add {g}{b} to your mana pool. Exert Fenbriar
Fortress unless it is a creature.
{7}{g}{b}: Earthshift 12.(If this land isn't a creature,
put twelve +1/+1 counters on it and it becomes a
creature.)
As long as Fenbriar Fortress is a creature, it has trample.