It's been said that the WAVING SNAIL is featured, at least for a few seconds, in every Adventure Time! episode. I've been re-watching my recordings, and so far, I've been able to find him in all episodes! Comment below if you can't find him in a certain episode or if you just wanna chat about how funny his different "hiding places"/mini scenes are!
Adventure Time! and its characters, of course, belong to Cartoon Network and Pendleton Ward :)