We had a similar situation with this guy tonight. We think that the NMs insane trait of healing up almost to full but getting progressively weaker is triggered by something. When we fought it Mamool had Astral Candy, but maybe magic or weapon skills cause it to heal somehow?
I think this NM glitched out on us... My PT, BLU BLU KrakenDRK WHM and RDM, fought this for 3 hours, wiping 2 times til we got refresh. We are now in a battle that has lasted 2 hours, we took it to 1% then it bene'd and his HP bar is stuck at 45% now... after 3 souleater kraken atempts we still havent been able to get his HP bar to move. Has anyone else had this problem?
Edit: And now it's moving again... Gosh this guy is a pain..