Sentinel's Flamekin

Flying
Whenever Sentinel's Flamekin enters the battlefield, if you spent {b} to cast it, exile the top four cards of your library. Then, manifest target face up artifact card. (In any zone.)
Sadness {2}{g} (Whenever this card is exiled from a hand or library, move it to its owner's graveyard. Then, its owner may cast it for its sadness cost. If they don't, exile it.)