Sorry to hear about your Oscar, Gee wouldnt have thought it would have fit in its mouth. Borneo tigers look as they have a little mouth. Its a learning game for us all, as some fish are ok in tanks with others some are not. Bad temperment comes with even the little ones.
I had a male Malwai eye bitter who wanted to eat every thing in his tank. (only a baby too) got rid of it, got another one,(large male, ) he swims with every thing no problems.it was just a fish with bad attuide, (like many of us people),