[Spoilers] Looking for help on a mod added area

A mod I have added a new area into ToB and I am not sure which mod did it? It is a dungeon under the witch area in ToB (Naylee, foster mother of Yaga Sura). The dungeon is full of poison gas and no party member can enter. I was wondering about a few things:

1) Which mod added this area? My guess is the Golem for Mages mod or the Chaos Sorcerer mod ( @argent77 ), but not sure.

2) How do you clear this area if no party member can enter (even with poison immunity)? I send in golems (and thus one of my mod guesses above), but they have a hard time in what I think is the final fight.

3) What is the gain from doing this area?