Iyara's Fortress

Iyara's Fortress enters the battlefield tapped.
{t} Add {g}{g}{g} to your mana pool. Activate this
ability only if you control three or more lands.
{x}{g}{g}{t}: X defending creatures you control gain
"when this deals combat damage to a creature, it
doesn't untap during its controller's next untap
step" until end of turn.