Super Shadow 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):

Super Shadow
519px-Super shadow final
Full Name Super Shadow
Current Age Unknown, possibly 56
Gender Male
Location Mobius
Current Status Alive
Class Neutral
Family and Relations
Main Weapon(s) Chaos Spear, Rings
Ability/ies Chaos Control, Flight, Invincibility, Chaos Spear
Vulnerable To None
Latest Appearance  ???

When the biolizard was threatening to crash into the planet after fusing to the Space Colony Ark, Sonic and Shadow used the Chaos Emeralds to transform, his fur turns a mach-gold, he can fly, with the given ability of a Chaos Spear, a long, sharp bolt of golden energy.

Sonic Battle 2 

Super Shadow is a the Alternate Coustume of Shadow. He is the 2nd Fastest Charcter but has the 2nd slowest dodge.