People already mentioned Onision, but only in regards to his staged videos, however, yeah, he pretty much hit the wall. His shtick was that he is an edgy boi and that's why teenage girls loved him, however, he is not a boy anymore, he is 35 and it becomes more and more apparent with each year. There is a lot of way younger and cute youtubers to stick to, so he is out of luck here. His content was never good in my opinion, but back then there was at least no strong competition, so he could get views. Today his content that doesn't revolve around his infamy gets 10k views at most, while channel has 2 million subs. He can't change this because his "comedy" is stale and unfunny. For some time he was claiming the videos about him, but since he lost YT partnership, he can't make money anymore, so no luck here. His reputation is beyond ruined, there are hundreds of videos about what a scum he is and the fact that even Discovery+ made a documentary about his degeneracy is quite telling. There is no going back from here, things can get worse only if he gets deplatformed or put in jail. Don't forget that he is also in debt, which he wouldn't be able to recover from even if his dead channels were monetized. Washed out, penniless and so hated, that his death will cause nothing but cheers.
I'd also add Shadman. He's always been edgy pedo degenerate, but back then he was huge, people knew him and he had a following even outside of his pedo shit. Now he is known only as the edgiest thing to mention in game chat and beyond that only by other degenerates. He is also a heroine addict, which is pretty much hitting the wall as it is, he will never fully recover from it even if he would want to.
