Roleplay Solo Dungeons - Can we just stop Square?

[Thi]

I'm currently stuck on the final boss in the 5.1 scenario in very easy mode. I even mapped keys to the pet bar, avoided all the visible AOE's, used the bit hit most of the time (#1), and the AOE attacks when the adds appear. I get him down to about 20%, and then the damage to him stops, but it increases on my character, and I die every time. Can't complete it, can't skip it. so I'm pretty much done with the MSQ.

I'm missing some kind of trick, so if anyone know it, please fill me in.

You need to use the limit break once it gets the damage invun.