Gwen managed to telepathically reach Ben inside the nightmare. By anchoring him to reality (referencing shared history/familial bond), she broke the mental lock. Upon waking, Ben triggered a transformation into Jury Rigg , utilizing the alien's intuitive intellect to dismantle the physical anchor of the Somnambulist (a corrupted Plumber beacon) while Gwen funneled all remaining mana into a sealing spell.