SPINY EELS + a knife and a mormyrid. In the right environment eels become extremely tame and personable, and the others are just super interesting. You could put an African knife with them, and then either an Elephant Nose or Baby Whale. Loaches are also one of my faves but they are not compatible with the Mormyrids, and probably they'd out-compete most the other stuff too unless you target fed. Add a school of small fish or maybe corys for activity and to bring out the oddballs and call it a day. You could even do a couple small cichlids. My personal favorite by far are Keyholes (#1) and I also like Bolivian Rams (#2) but Rainbows, GBR, Curviceps would all work as well.