Utapau

As Cavern of Souls enters the battlefield, choose a
creature type.
{t}: Add {c}.
{t}: Add one mana of any color. Spend this mana
only to cast a creature spell of the chosen type, and
that spell can't be countered.

"I took a trip to Utapau to explore the sinkholes.
Fascinating how the creatures of that planet have
adapted to live below the sssurface." -Charr