Paratilaipa Buttikoferi is the meanest fish I've ever owned. Meanest fish my uncle kept as well, at just 8" it went toe to toe with much larger fish (my uncle had a really, really mixed tank when I was little, this was over 20 years ago the hobby has gotten smarter since then).
This 8" butti would attack a 13" Jag, he was so furious in the tank my uncle moved him with his electric catfish, and it even tried to beat up the catfish while getting shocked... It was relentless.
Being enthralled by that fish when I was younger, finally I had a dumb mixed tank of my own (mostly "mixed" african's, and a large 12" pike cichlid of some type). Mine was the smallest fish in the tank, and every morning i'd wake to find something floating and the Butti fighting with the pike (which he couldn't beat when he was 4 1/2").
Also, keep in mind. Both these tanks were mixed poorly, all fish got along but I wouldn't advice mixing most of the fish my uncle mixed (from the dark days of aquaria) or the dumb things I did when I was young and dumb (putting Butti's with anything).
Hope this helps.