I just beat the avatar (again!) as a rogue! I used CYDSTEPP on the demon lords, but beat the avatar without even using CYDSTEPP by using a combo of whupaz first hit. Then badge of courage and reflex potion. Next, a quicksilver dodge (Used at beginning of fight) and then a first strike hit!
I have also beaten every normal boss (Tormented one and Tower of Goo included) with the whupaz, reflex, quicksilver combo!
I think this must be weakened because you can even beat the high damage dealers just by using a reflex potion and a quicksilver dodge!