My group wished themselves transported directly to the room with the tree of shackled souls and skipped most of the dungeon. I could have made up some way for the wish to not work as intended, but I didnt because it was great idea in the spirit of acomplishing the mission (e.g. stop the ritual from completing ASAP). They did major buffing before using the wish, but the final fight was still challenging because I had already planned to have Dyr'yd, Allurad, Shebbleth, Fish, Embril and a spellweaver in the tree room.
The drawback of their good tactics was that they never had a chance to find out about the dispersal collar. They destroyed the tree and Cauldron was destroyed in the volcanic erruption. Now they are talking about trying to get the Cauldron refugees to resettle on Occipitus!