We pulled last night for over 2 hours (didn't go too deep into the tunnels) and only had one of these guys show up to be pasted. He also dropped the Pine Shaft Pike (see stats below).
We had two pallys (myself 52 and another at 44) and we just alternated stunning them. Very effective, and we prevented lots of unknown damage and heals as he rarely stopped trying to cast.

Gnoll Canine
Mithril Knuckles
Pine Shaft Pike