The pool scene was incredibly risqué, for that era
https://i.imgur.com/yfMBxxF.jpg
https://i.imgur.com/TQPNiKK.jpg
https://i.imgur.com/brmJEAr.jpg
The nipples of Marceline are as clear as Day. We wouldn't even see that in a 2022 mainstream movie... almost.
I understand it's a pre-code movie, but still!