Tartarus, Monster Spewer

When Tartarus enters the battlefield, sacrifice
it unless it escaped.
When a creature that has escaped deals
combat damage to a player, copy a card with a key counter on it and remove a key counter from it,
you may cast the copy without paying
for the mana cost.
Escape-{3}{b}{r}{g}, exile seven other cards from
your graveyard.
Partner with Thanatos, Underworld Jailor