Cavern of Souls

As this land enters, 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.

Dragonlord Atarka

Flying, trample
When Dragonlord Atarka enters, it deals 5 damage divided as you choose among any number of target creatures and/or planeswalkers your opponents control.

Destructor Dragon

Flying
When this creature dies, destroy target noncreature permanent.

Balefire Dragon

Flying
Whenever this creature deals combat damage to a player, it deals that much damage to each creature that player controls.

Atarka, World Render

Flying, trample
Whenever a Dragon you control attacks, it gains double strike until end of turn.