Ok guys,
I found even more stuff that I didn't even know about, and there are some interesting things there, like the fact that the boxing ring's background design from Gus's mix is a redesign of the battle arena from Robot Love, but there's another thing I wanna talk about:
I don't think you know, but sometimes I change the abstract filenames in some of the backgrounds into simpler ones, in order to upload them way easier here. Things that I didn't change their filename are for example, some of the Affenkugel Castle backgrounds and Culpepper's office (known in its filename as "Dr. Friedman's office). There's even the Affencoaster from Wunderpark, which I don't think had a name in the show.
But, in some backgrounds of Affenkugel's castle, there is a certain word that I originally thought it's an alternate name of Affenkugel or his castle: Affenschloss. Turns out schloss is German for castle, but I don't think that's the castle name, because like the Affencoaster, it was unnamed in the show. It's probably just a nickname the designers slapped into the filename.