I forget what level I was (on Normal), but I did it with a solo Agent, and the key was to avoid its area spell, and only get hit by its breath. It took a bit of luck, but I first shackled it (also wracked, I think), then set acid and energy status, then ran like mad.
Poison, acid, and energy feel way more powerful than in previous games, especially combined with regeneration. I got through a lot of potentially maddening stun-locks by buffing up, running in and casting acid shower, then hunkering down and letting the enemies slowly die. This worked even better on non-stunning enemies, since you could afflict them with all 3 ailments.