Wow! I’ve never seen a tank like that before. It’s really cool! Are the back and front sections entirely separate? How many gallons is each part?
As long as you pick something that’s not at high risk for jumping or climbing out (bettas or mystery snails need lids for these reasons), you should be good. If you like invertebrates, it could be cool to keep a colony of neocaridina shrimp or perhaps one of the beautiful freshwater lobsters (as long as they stay separate from the mollies, who might snack on baby shrimp or be terrorized by the lobster). I’d still keep the water level low and keep an eye on them, though, since I’m sure a determined invertebrate could climb out.
If fish are what you’re looking for, as long as you don’t pick a particularly jumpy species and you don’t fill the water all the way to the rim, you should be fine.
