Uroboros of Eternal End

Haste, Deathtouch.
Whenever an Opponent's creature or land is destroyed or discarded, exile X cards from their graveyard once this round. User gain {x}: X is equal
to that card’s mana cost.

When destroyed or sacrificed, revert it back into
Ankh of Eternity, +3/+0 counter upon its next transformation, stacks. All Players loses (3+R) life:
R is equal to the number of times it has reverted.