So had to find Arreat Summit again. Worked through nasty lancers, cold carvers and their resurrectors and the pin cushion beasties.
BoBo prefers to take the bulls by the horn, those quillrat have bad poison and are nasty and BoBo must keep up shield until decrepify processes, then Bear Rage takes over. So, found this place again:

Trying it out with the Barb using decrepify. Halgaunt gets crushed. Notice the steep learning curve...this time BoBo got prebuffed.
Don't miss the mana pots distributed on the right...more south and west:

Probably tried this thing 10 times. Dang. Seems the Whorlwind barb really hurts the party. Trying to think of a way to minimize his effect. Maybe fight nearer the edge in tight areas ? Problem is, Halgaunt seems to be their target and he can't tank.

Anyways, even took Halgaunt out in bloodmoor to get him faded and find more rejuvs. There was 1 time when the Bear Gang seemed to have the upper hand but mana drainers won out and got Halgaunt. Couldn't deal with then all.
Main theme was to get them decrepified and then switch to Beast.