is he the one that spawns in the water?
in that room on the map labed (4) ? if you look around youll be like i dont get it, there is nothing here.. but if you like swim into that fountain, there is a static spawn in there, iirc i was like THERSE THE FUCKER I WAS LOOKING FOR FOR THE LAST 3 HOURS
not sure if thats same mob though was ages ago.