Since the Characters are the "leveled up variations", thanks to "Imagination" and "Memorization" of Silent "Player-On!" once she accepted the Game Rules of Dr. Golden
(Maniac Mania "Different Dimension" after this event morphed into Fiercy Forces),
there will be some slight revamps to fulfilly, complete and make more suitable changes to the names of Characters and their "code names" as well.
The List of Characters that are and are confirmed to be in "Imagine It!" Comic series.

FNaS: WM "RoR" = Five Nights at Sonic's: Widerise Mingleverse "Route of Recollect"
FNaS: FF "II!" = Five Nights at Sonic's: Fiercy Forces "Imagine It!"

Note: Not all Characters are mentioned or names revealed in this list for Not spoiling purpose.

Cast of FNaS 1: WM "RoR" and in FNaS: FF "II!"

Clone Sonic "Tune-Up!"
Clone Mario "Tune-Up!"
Clone Yoshi "Tune-Up!"
Clone Tails "Tune-Up!"
'15 Golden Sonic "Memorize-Up!"
Clone Mighty "Hunt-Up!"
Clone Ray "Hunt-Up!"

Knuckles "Recall-Up!" / Security Guard Knuckles

Cast of FNaS 2: WM "RoR" and in FNaS: FF "II!"

Mechano Toy Sonic
Mechano Toy Mario
Mechano Toy Yoshi
Mechano Taingle
Mechano Balloon Toad
Mechano Luiginette
Withered Sonic "Sore-Up!"
Withered Mario "Sore-Up!"
Withered Yoshi "Sore-Up!"
Withered Tails "Sore-Up!"
'17 Golden Sonic "Memorize-Up!"
Mechano Toy Tails
Tails Doll "Stitch-Up!"
Paper Plates "Reshape-Up!" ~ "Paper Sonic & Paper Mario"
The Shadow Team "Triple-Up!"

Amy Rose "Remind-Up!" / Security Guard Amy

Cast of FNaS 3: WM "RoR" and in FNaS: FF "II!"

Salvage Sonic "Gory-Up!"
Phantasm Mario "Jeer-Up!"
Phantasm Yoshi "Jeer-Up!"
Phantasm Tails "Jeer-Up!"
Withered Mechano Toy Sonic
Withered Mechano Toy Mario
Withered Mechano Toy Yoshi
Phantasm Mechano Taingle
Phantasm Mechano Balloon Toad
Phantasm Mechano Luiginette

Modern Sonic "Reversion-Up!" / Sentinel Martial Artist Sonic
Silver "Reversion-Up!" / Sentinel Martial Artist Silver

Cast of FNaS 4: WM "RoR" and in FNaS: FF "II!"

Nightmare Sonic "Dire-Up!"
Nightmare Mario "Dire-Up!"
Nightmare Yoshi "Dire-Up!"
Nightmare Tails "Dire-Up!"
Nightmare Golden Sonic "Memorize-Up!"
Mechanight Toymare
Phantasm Salvage Sonic "Fleer-Up!"
Phantasm Amy "Residual-Up!"
Night Terror Sonic - aka. Insomnic
Plushnic & Plushtails "Hum-Up!"

Luigi "Superstellar-Up!" / Security Guard Luigi

Cast of FNaS 4 DLC: WM "RoR" and in FNaS: FF "II!"

Nightmare Mechano Toy Sonic
Nightmare Mechano Toy Mario
Nightmare Mechano Toy Yoshi
Nightmare Mechano Taingle
Nightmare Mechano Golden Toy Sonic
Nightmare Salvage Sonic "Creepy-Up!"
Nightmare Mechano Luiginette
The Lunighttemare "Ominous-Up!"
Plushrio & Plushi "Boo-Up!"

Cast of FNaS 5: WM "RoR" and in FNaS: FF "II!"

Origin Sonic "Midday-Up!"
'15 Golden Sonic "Memorize-Up!"
'17 Golden Sonic "Memorize-Up!"
'22 Golden Sonic "Memorize-Up!"
'27 Golden Sonic "Memorize-Up!"
Nightmare Golden Sonic "Memorize-Up!"
Shadow Sonic "Midnight-Up!"
Dr. Golden "Prepare-Up!"
(This confirms that he appears in FNaS 5: WM "RoR" as well and he's the part of the "Golden Sonic Team")

Plush Origin "Morncloud-Up!"

Classic Dr. Eggman "Scheme-Up!" / ???

Classic Tails "Genesis-Up!" / Security Engineer Tails
Classic Sonic "Genesis-Up!" / ???

Cast of FNaS 6: WM "RoR" and in FNaS: FF "II!"

Floral Lefty Sonic "Rosace-Up!"
Fortunate Mechano Righty Sonic "Clover-Up!"
'22 Golden Sonic "Memorize-Up!"
Mechano Golden Toy Sonic
Mechano Confetti Toadette
Nightmare Amy "Ghastly-Up!"
Gizmo Gear Mechano Sonny

Cast of FNaS: FF "II!"

Dr. Golden "Prepare-Up!"
DJ Stellar Espio
Top Stellar Shadow
Memorial Infinite
Leo Metal Sonic
Counterfeit X
Abyss Crystalline King Boo
Glitchnic "Hack-Up!"
Clone Sonk :) "Smile-Up!"
The Bomberman Team ~ Bomberman "Whiteness-Up!" &
Bomberman "Blackness-Up!"
Zeo Metal Zee
Shinobi Pac-Man
Giana "Twin-Up!"
Fiery Giga Bowser
Phantasm Luigi "Sneer-Up!"
Spectrum Ian "Aftermath-Up!"

Silent "Avatar-On!" & Silent "Player-On!" / Security Guard Silent &
Soldier Grandeur Silent
Shadow "Rely-On!" / Specialite Agent Shadow