The Skull Egg Zone is a Zone made by the combined efforts of Dr. Eggman and Dr. Wily, during the Sonic & Mega Man: Worlds Collide cross-over event. It is a pocket dimension that links Mobius Prime and the alternate planet Earth in the year 20XX.
The Skull Egg Zone's possesses unique temporal traits that makes time pass differently in this dimension, in that hours that pass here amount to mere seconds on Mobius Prime and on the alternate Earth in year 20XX.
The Skull Egg Zone was created by Doctors Eggman and Wily, after the two doctors came into contact with one another, in order for the two of them to meet and work on their plans to take over both of their worlds. Using the theories provided by Dr. Eggman, Dr. Wily was able to create the Skull Egg Zone with the Chaos Energy from the blue Chaos Emerald that had ended up in Wily's world following Operation: Clean Sweep.
After meeting with each other, and deciding the name for the Skull Egg Zone (Eggman wanted to call it the "Egg Pocket Zone", and Wily wanted to call it the "Skull Secret Zone"), Eggman and Wily used the Skull Egg Zone to secretly construct the Wily Egg, without the fear of limitations or interference. From within the Wily Egg in the Skull Egg Pocket Zone, Eggman and Wily then released the Genesis Wave on both the doctors' worlds, reshaping both realities to their benefits, with the zone serving as an area where the two of them could remain immune to the waves' effects.
The Skull Egg Zone is a seemingly desolate dimension, devoid of any life. In its first appearance, the surface in this dimension is checkered brown, much like soil in the Green Hill Zone, with mechanical devices merged to the ground, and possesses a pale, greyish green sky with thin clouds.
- The name is a direct combination of Dr. Wily's and Dr. Eggman's insignia.