I’d recommend any kind of catfish like 4 line pimelodus, syndontis cat, striped Raphael, since oscars make a decent mess and a catfish wouldn’t interfere with the Oscar. Also, I’ve seen people house oscars with larger schooling/shoaling fish like Baka sharks, tinfoil bars, lemon bars, Phoenix barbs, etc. this would also make the tank and fish more active since they swim around constantly. I’ve also seen people keep oscars with Geophagus, severums, and other less aggressive cichlids with no issues. If you want an Oscar “community” getting the fish I mentioned should be fine. However, if you are serious about breeding them, it’s best to keep them alone or with some of the bottom dwellers mentioned. Again, some of the fish i mentioned may get to big for the 100 gallon term so if you don’t plan on upgrading to 150 gallon + I’d just recommend keeping the Oscar Pair and maybe a catfish!