Mysterion

Improvise (Your artifacts can help cast this spell.
Each artifact you tap after you're done activating
mana abilities pays for {1}.)
If Mysterion is exiled, sent to the graveyard or
returned to your hand from the battlefield in any
way return him to the battlefield with a tired
counter. {w}{w}{b}{b}: Remove all tired counters.
Sacrifice Mysterion: Destroy Target creature with toughness equal to Mysterion's power or less.
Creatures with 4 or more tired counters can't be sacrificed or attack.