Sedgemoor Witch triggers, creating a 1/1 Pest creature token.
Resolve Essence Flux, blinking Skullwinder.
Skullwinder enters the battlefield, returning Essence Flux from your graveyard to your hand and causing target opponent to return a card from their graveyard to their hand.
Activate Phyrexian Altar by sacrificing the Pest, adding ({U} magic symbol) .