It may help to do cartoon network characters by show! So like "adventure time" "the regular show" etc for different categories since there are no hints or anything. The first few characters I typed in were classic cartoon network characters but you didn't have listed (courage the cowardly dog, johnny bravo, billy from billy and mandy etc). It may also help to specify "Cartoon Network characters 2015-2020" or whatever the time period is so old 20-something fans like me aren't disappointed lol.
I would add Ice King for Adventure Time and Skips, Pops, Benson, Muscle Man, Margaret, CJ, Thomas and High Five Ghost to Regular Show. Just the two slackers feels a little low.