I'm also thinking of adding the Addiction from Afraid of Monsters as a boss recommendation.
Addiction:
Rage: Chain Lightning - Anyone caught in a close radius will have their health drained away.
Super Rage: Minions - When super rage is cast, all dead players will be forced onto the addiction's side and will fight in a monster form (from AoM if I can get the ported models). The song 4motherkill.wav will play when triggered.
Attributes: Can spawn with Book Simon on a random occasion. He has a slow attack rate, but is a bit faster moving. Normal super jump.