The very immediate problem of your fan fiction is it's too dark. Remember that grimdark in a supposedly kid-friendly setting like Sonic the Hedgehog (or cartoon animals in majority) will be easily subjected to criticism. I'm not saying it's not do-able, but you need to be extremely careful dealing with your story and you need to make sure you'll leave certain message or moral that can invoke positive reactions from the readers, toward the story, the characters, and toward you as a writer.
Writing a "human god" character who's also borderline insane is a very tricky thing to do. you cannot just torture the animals graphically without a reason: there's a risk of you going too far that the grimdark overshadows the plot and the message you're going to convey. On the other hand, you cannot write this kind of story without taking a peek at a psychological aspects of the characters: things will go too light and will make the whole thing not interesting. Your narrative needs to generate enough tension and empathy to "hook" the readers to stay until the end.
Personally, I don't recommend it. If you screw up by making characters too sadistic, out of characters, or/and even fail to deliver the meaningful ending and message to the readers, it's Sonic's reputation that will suffer the most. However, this is your choice. If you're really going for it, I recommend you reading some of short horror stories, particularly made by Edgar Allan Poe like The Black Cat or The Tell-Tale Heart, to enhance your techniques in writing the psychological horror genre.
I wish you the best of luck and writing development.