He appears in one page of Tales of the TMNT #5 as a Watcher type parody on the first page of the issue to drop some Watcher-Stan Lee-Rod Serling monologue intro for the story to follow.
The actual story is about some mutant bad guy gargoyle looking dude who fights a female superhero named Radical, and after they crashed the city up a bit, April and the Turtles show up to close him out.
It was just a gimmick to do more commentary on superhero comics.
The domoids who are included with him don't even appear until issue 15 of that book.
You know how the original Ninja Turtles sketch was just a parody of the concept. Same vibe.
In respect to your specific question, which I do appreciate the specificity of as a neurodivergent, he is not a character that lives in the universe, and he is not a character that is fictitious within the universe. It is just a splash page gag.
So if all of this is Greek to you, unless you think he's cool, I think it's a safe pass. Here in Canada, EB wants as much for him as they do Leatherhead and I just don't accept that. I don't know if that's the case for the US pricing?