The Classic Version: Alter Shadow Sonic
from Five Nights at Sonic's: Mega Merge Max Mix
(Alternative Maniac Mania - "Extra" Comic)

As you can see he has received more resembling appearance from Fierce Forces (Golden Glow).
But still can change the look to his previous one, as a Skin: Anterior Shadow Sonic (Snowy Shine).

Then he will later turn into The Modern Version: Shadow Sonic "Midnight-Up!"
And appears in Five Nights at Sonic's 1-6: Insane Immerse
(except FNaS 4 DLC: II)
(Pizzerias on South Island - Addon Comic) /

Five Nights at Sonic's: Fierce Forces "Imagine It!"
(Fierce Forces Arcade Machine in Dr. Golden's Prep Mean Haze Citadel on Angel Island - Main Comic)

Shadow Sonic "Midnight-Up!" appears in (Fangames):
Five Nights at Sonic's: Fierce Forces "Surreal Show-off!"
as the alternative personality: Reverie Stellar Shadow Sonic.

Fervour Daybreaks at Sonic's: Fierce Forces "Aureate Afterglow!!"
in his default appearance (Golden Glow) and also...

Five Nights at Sonic's: Fierce Forces "Entertain Entrapment!?"
but in an alternative look...

As: Shadow Sonic "Midnite-Up!" (A resemblance of his previous look (Snowy Shine))

Fun Fact: And yes, I once made a post that this Skin will not appear in "Aureate Afterglow!!" fangame, yet only in "Imagine It!" comic as a something extra.
But changes have appeared and I decided, that in "Entertain Entrapment!?" this one will be as an "Unique" Skin.
And... to show an origin of the Skin, not only related to the past, but as a morphed look in Majestic Mission Arcade Machine, because of an event)