The title is "Who is the meanest baddest fighting machine" IMO it take two fish to answer this question "Meanest" Red Devil, "Baddest fighting machine" a full grown male Dovii.
The Dovii is much more powerful than a Red Devil. I saw this video on youtube of a guy keeping the two and look how easily the Dovii over powers a male Red Devil, who is guarding fry. The Dovii is probably only being semi aggressive here. There are three parts....