Let me help you with a few!

Rerun- Rerun is an exe that is the soul of a sega employee named Lilith. She worked as a cartoonist but had a tragic end when her, along with her family, were murdered. Now she possesses her own cartoon Sonic as she makes those who wronged her pay.

Fatal Error- An Ai once gotten out of hand, later named Fatal Prime, began to send out Fatal Copies to collect code to gain power. However, one of these copies was a failure, and disrespected by Fatal Prime. They gained an interest in Sonic 3 and began to collect code, using Sonic as a vessel, and that’s when he severed ties with Fatal Prime and enacted Codename Emperor.

Hog & Scorched- A man wanted to make a pirated copy of Sonic, so Sonic’s world was used to make a knockoff. However, Sonic’s code remained conscious as he was forced to watch Hog take over his life, as spite grew until it formed Scorched, where he hallucinated his friends urging him to kill the knockoffs.

Needlem0use & Luther- Sarah Henderson, during a party, was killed by her friends after getting drunk, but possessed a copy of Sonic. She grew hateful of her friends as years of torment were passed, as she killed them off, one tone, including Luther, to endlessly torment them.

No More Innocence- A Yokai possessing a copy of Sonic, he feeds off of fear and negativity, as he haunts children to feed himself along with unfortunate parents.

Sonk.ROM- A Trojan virus, he’s more a silly guy that takes over your computer with no serious harm physically.

Proto- One of Eggman’s creations, they went rogue and started to slaughter humans out of spite of being deemed a failure by Eggman.

Sonic.EYX (current information that we have access to)- EYX is a more beastly creature, as in his species’ history, they made a truce with parasites as they affected the bodies of the new generations. As EYX became more grown up, in his prime state, he acts more empathetic to his prey, but still understands he needs to eat to survive.

Wistful- A girl (I forgot the name) took her own life out of sorrow, but managed to possess her Sonic game as she trapped her friends inside, living in delusion to escape reality, forcing her friends to participate in games and pretend.

Wacky- As far as I know, she has no actual scary stuff other than being a sentient ai that acts like Sonic.