|Eggman Nega did not originate from fanon, and more information can be found on their respective wiki(s). You may read more about it on the following wiki(s):|
Eggman Nega is the parallel version of Dr. Eggman that has appeared in the Sonic the Hedgehog series. He came from the same dimension as Blaze. He is a lot smarter than his counterpart, but also more insane.
Eggman Nega has a huge role, as the main enemy in the Sonic Speedball RPG (Dr. Eggman makes no appearance what-so-ever) who is trying to collect all the Chaos Emeralds to finish building Mecha Shadow, (also known as Metal Shadow) an advanced version of Metal Sonic.
Eggman Nega reappears in Sonic Speedball RPG II: The Coming of Chaos! but this time with minor role of helping Chaos destroy the world. At the end the player is expected to believe that Nega is a good guy when he helps Sonic and friends defeat Chaos.
Eggman Nega will appear once again but this time he will take over the world and form an empire.
Fighting In His Own World
He appears as a secret boss in Micool's Second Quest. You find him in the Nega World/ 9th World.