All knifefish hide a lot...so those are pretty much ruled out; unless you keep the light off or dimmed. You could try some clown loaches, tinfoil barbs (even though they aren't oddballs), rope fish, redfin prochilodus, zig zag eels, banded leporinus, rainbow snakehead, a hujeta gar or any other small gars
cuban gar
tropical gar
tsn
lungfish
asian arowana
peacock bass
xl fire eel
payara
rainbow snakehead
rope fish
dolphin mormyrid
african arowana
sterlets
dragon knifefish
discus fish
mbu puffer ( maybe )
datnoid
severum
fly river turtle ( maybe )
other bichirs
baby whale
all of these fish could work if they are under 10 inches