These mobs float around the cavern level of Befallen: Cavern of the Afflicted and cast Fear of Darkness whenever they get close to a player. The spell makes the target afraid and roots them. To dispel the darkenings, get the torch on the wall by the entrance (there is no way back up, except evac, if you forgot to get the torch) and light a mysterious stone altar, at 109, -60, -82.5 , in the water.