It's basically a collection of the really fucking terrible things that he's said as "jokes", from his use of blackface and racial slurs to actual bestialityand the just overall terrible ways he's treated children in his skits.
Spoiler - click to show.
Notable standouts include pretending to masturbate to then-11 year old Willow Smith, this really fucked up puppet show he did with the Fine Bros called Hey Millie that was about an 8 year old puppet being put in super uncomfortable situations, general sexual comments on kids ("skinny little sexy six year old", talking about Rebecca Black's breasts when she was a kid, etc.), his "justification for pedophilia" from his podcast, and–of course–the cat thing.
It's…a lot. There's a really good Twitter thread that cites a ton of it, I think MissHemlock was the name of the person who compiled the big one?