Looking for cool Hardy oddball for cichlid tank!?

[Marlino]

i have a south american cichlid tank with it having a 5 inch oscar. im looking for a hardy or decently easy to care for oddball. plecos and knifefish are out of the question. i wanted a fire eel but cant seem to find one in stores any other oddballs that i could get? it needs to be big (of course) so my oscar wont eat him. i want to have an unusally fish in my tank ive considered stingrays(which is now out of question cause of size, and special care) and also puffers ( dont seem to find one big enough and they are dirty but i was wondering if there just as dirty as oscars cause if so i could get one if i find one big enough cause i have a 150 filter running in a 90 gallon tank. so yeah. thanks in advance please stat fish common names and food.

[Boring Sponge]

freshwater sting rays are cool, arowanas

[Stuey]

Get some bichirs, featherfin cats,