12 mana and a 12/12 trample every turn

, Sacrifice a black or artifact creature: Add an amount of equal to the sacrificed creature's mana value.

Whenever another creature enters, you gain 1 life.

Trample When this creature enters, sacrifice it unless you sacrifice any number of creatures with total power 12 or greater.

At the beginning of your upkeep, you lose 1 life. At the beginning of your upkeep, you may return target creature card from your graveyard to the battlefield. That creature gains haste until end of turn. Exile it at the beginning of the next end step.

Creatures entering don't cause abilities to trigger.