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 Phyrexian Altar by sacrificing Fatestitcher, adding one mana of any color.
Choose to exile Fatestitcher using Void Maw's replacement effect instead of Fatestitcher's.
Activate Void Maw by putting Fatestitcher from exile into your graveyard, giving Void Maw +2/+2 until end of turn.