The "Dying" in their name refers to their fragile state as well as their skills. With only 90 health, literally two or three blasts of a staff or wand will kill them. Also, left on their own devices, their two skills involve a significant amount of health sacrifice. Often they will kill themselves trying to remove enchantments or BiP their allies.
Although there are many wandering in the open with other patrols, most often Grasping Darknesses or Aatxe, they are even more commonly found hidden, only to pop out of the ground when an enemy ventures near. Unlike most pop-ups however, these creatures often patrol with nearby units once spawned (in the unlikely event they survive their first encounter with an enemy).
These creatures can be the most pitiful or most dangerous creatures in the Underworld, depending on who they target and how much that target depends on enchantments.
They are significantly more resilient in hard mode, with 60 armor and several hundred health. They are still relatively weak, but their wand attacks can do a decent amount of damage if not taken care of.