The Succubus is an uncommon enemy only found in Hell.
If she manages to pounce on the Spelunker, she will cling to them like a Monkey and take one hit point when she jumps off.
The Succubus mimics the appearance of the currently selected damsel type, disguising herself as a female, male, dog or sloth. Regardless of the disguise, she always transforms into a demonic woman upon attacking - there are no male, canine or sloth Succubus models.
The Succubus' attack is accompanied by a loud "scare chord" sound effect that persists until she is killed. Her most dangerous ability is to stun and push the player when she jumps off (like a monkey), and she can continue attacking the player while they are unconscious.
Disguised Succubi are non-aggressive from a distance, so avoiding apparent Damsels you find in Hell will mean you won't have to deal with them. However, this strategy results in forfeiting possible hit points for saving any genuine Damsels that appear. A camera will kill her instantly. If she clings to you, simply use a rope to neutralize the threat, and you'll take no damage (this only works if there's space above you).
It is difficult to positively distinguish a Succubus from a genuine Damsel. On average, Succubi call for help more frequently, but both Succubi and Damsels call for help at randomized intervals, making it difficult to be certain.
The easiest way to identify a Succubus is to use a Camera on her; as an undead monster, a Succubus will be killed instantly by the camera flash whereas a real Damsel will only be harmlessly stunned. Similarly, landing on a disguised Succubus from above will kill her via stomp damage, while a Damsel will be unharmed.
Although it is of little practical use, it is also rather easy to discern Succubi from real Damsels posthumously. If you kill a Succubus from a range (for instance, with a shotgun), she will crumble to dust without leaving a corpse. The body of a genuine Damsel, however, will remain after death (unless she is killed with the crysknife, freeze ray, or if she is crushed or telefragged).