You control a permanent that can tap to produce at least ({U} magic symbol) .
Steps
Activate the mana-producing permanent by tapping it, adding ({U} magic symbol) .
Activate Fatestitcher's unearth ability by paying ({U} magic symbol) , returning it from your graveyard to the battlefield and giving it haste until end of turn.
Activate Fatestitcher by tapping it, untapping the mana-producing permanent.
Activate Carrion Feeder by sacrificing Fatestitcher.
Choose to exile Fatestitcher using Void Maw's replacement effect instead of Fatestitcher's.
Resolve the Carrion Feeder ability, putting a +1/+1 counter on it.
Activate Void Maw by putting Fatestitcher from exile into your graveyard, giving Void Maw +2/+2 until end of turn.