Zona Fantasma
In "Superman/Wonder Woman", Doomsday mysteriously appears in the North Atlantic Ocean and fights Wonder Woman, breaking her arm before vanishing. After describing her attacker to Superman, both travel to the Fortress of Solitude where Diana identifies Doomsday on a Phantom Zone viewing device. Superman assumes that the walls of the Phantom Zone are failing, which has allowed the momentary escapes for Doomsday.