Kroulus, sun of Gaea

As an additional cost to cast Kroulus, you must sacrifice a creature
When Kroulus enters the battlefield, sacrifice X lands, exile them under Kroulus
{t}: Add mana of any color in any combination equal to the number of lands exiled under
Kroulus
{1}: Sacrifice Kroulus, deal X damage to any target
where X is twice the amount of lands under Kroulus