The Skull Egg Zone is a pocket dimension between Mega Man's and Sonic's universes that Dr. Eggman and Dr. Wily collaborated to make by using Chaos energy from the blue Chaos Emerald. It is under a time dilation effect, which allowed the two doctors to complete the Wily Egg without drawing any undue attention from their absence in their home universes. The two doctors arrived here through the Interdimensional Gateway.