Kemuel's Nightmare

Kemuel's power and toughness are equal to X.
When Kemuel enters the battlefield, target X
artifacts on the field. For each of those targets,
exile a card with converted mana cost equal
to that artifact from any player's graveyard face
down. Whenever any of the targeted artifacts
leave the battlefield, play any one of the cards
exiled with this effect without paying its mana
cost and ignore any timing rules or limitations.
Kemuel's wing and leg rest in it's stomach...