It also *SPAMS* the following proc like effect "Curse of Eternal Suffering". It would proc that between once every 6 or so seconds up to 4 times a second. It lowers ATK by 300. It checks on MR with -1000 to the check. If you're the MT, leave a buff slot open as it isn't going away.
A Possessed Warlord also has that same proc, but the rate is much slower, maybe 1/4th the proc rate of the Warmaster. Again, if you're the MT, leave a buff slot open.
Lastly, judging by my parse, I'm 90% sure that it was holding an Icy Greatstaff, but not sure. Will post more info as it comes.