There are theoretically an infinite amount of succubi in the Abyss. These fiendish entities are tanar'ric creatures that feed upon the life forces of mortal men, doing so with diabolical supernatural powers acquired when they either manifest fully formed or evolve from lower tanar'ri.
Tanar'ri Physique: succubi are not fighters, per se, though they're tanar'ri nonetheless. These powerful demons possess a large array of powers as a result, allowing them to engage in battle if they must. Succubi possess these tanar'ric capabilities:
* Darkness: all tanar'ri have the ability to share the inherent darkness of their very souls with the world at large. This rudimentary power functions at but Poor (4) rank, but basically 'blacks out' the area a succubus currently occupies (it works within Near range).
* Damage Reduction / Cold, Magic and Physical Attacks: though they prefer not to do battle, a succubus is a rather tough creature. They possess 2 CS of damage reduction against all physical and magic attacks, as well as cold-based assaults as well.
* Dimensional Transit: in addition to being able to teleport, succubi can transition themselves between planes of existence (above and beyond the normal tanar'ric teleportation ability). They may do so with Excellent (20) ability, the better to find mortals to prey upon.
* Infravision: many of the Abyss' countless layers are dark beyond mortal ken, and have never seen the light (physically or otherwise). As such, all tanar'ri have evolved the ability to see by heat as well as by visible light, and can do so with Good (10) ability.
* Invulnerability to Fire, Electricity, Heat, and Poison: the tanar'ri are hardy creatures - they have to be to survive at all in the endless, horrific wastes of the Abyss. Their forms have evolved over time to give them complete immunity to fire, electricity, heat, and poison.
* Portal Sense: planar beings all, succubi have the ability to perceive the various rifts that dot the planescape of the multiverse. Most of these doorways are invisible to the naked eye, but all succubi can spy them with ease, doing so with Excellent (20) ability.
* Telepathy: almost all tanar'ri are able to communicate directly from mind to mind - a vital skill when so few speak the same tongue. They can usually broadcast and receive thoughts at Typical (6) rank, enough to get their point across when necessary.
* Teleportation: chaotic creatures all, the tanar'ri can bend space itself to their will. All tanar'ri possess the power to teleport with Remarkable (30) ability, and can avoid teleportation's usual side effects while transporting themselves within the same plane of existence. *
Additional Limbs / Wings: in their natural form, succubi possess large, bat-like wings. These large, leathery extensions of their body are not equipped to attack or handle objects at all, but allow the creatures to fly at Typical (6) speeds, or 90 miles per hour.
Charm: succubi possess the ability to charm a single target, per the spell of the same name. This skill lets them make temporary 'friends' of those who fail a Psyche FEAT roll against this Excellent (20) ranked power, until she attacks or they can break free of it.
Clairaudience: this dangerous power allows a succubus to eavesdrop on targets far, far away. Functioning on the Far range table, this Feeble (2) power enables the succubi to listen in on sounds up to one mile distant, assuming they know precisely where to 'look'.
Danger Sense: the teeming masses of succubi are rarely, if ever, surprised by anything in their environment. They possess this supernatural awareness of their surroundings at Excellent (20) rank, which informs them of any dangers, active or passive, that threaten them.
Disguise: at will, a succubus may assume the form of any humanoid being within their size frame (nothing smaller than half their size, nothing larger than half their size again). They may do this with Good (10) ability, usually posing as particularly beautiful females.
Intangibility: succubi all have the ability to render themselves intangible, at will. This Remarkable (30) ranked power causes physical and energy based attacks to harmlessly pass through them, which is usually enough to avoid conflict with simple mortal beings.
Mesmerism: all succubi possess a limited form of mind control. They may direct a target to engage in any reasonable activity they desire, and their foe must resist this Excellent (20) ranked power or comply. Of course, obviously fatal instructions automatically fail.
Summoning: once per day, a succubus may attempt to summon forth one balor to aid them. This is but a Feeble (2) ranked power, meaning the odds of it succeeding are not very good, but if it does, a succubus has a considerable 'trump card' to rely upon in a tight spot.
Vampirism: perhaps their most notorious skill, succubi have the ability to feed off of the energies of others. They can do this with Good (10) ability, which allows them to drain like Health from a target with each attack - the trick is this ability is subtle.
While she must touch her target for this power to work, those affected by it must pass an Intuition FEAT roll to even notice it has been used against them. This is why the succubi prefer to lure mortals into moments of passion, thus distracting them (-2 CS to the detection FEAT).
Limitations / Enhancements:
Susceptibility: like all tanar'ri, succubi are weak against the use of cold-wrought iron weapons, as well as holy water and weapons. Their supernatural defenses are ineffective against such assaults, which inflict at least a quarter of their maximum Health in damage.
Attractive: the succubus always exists in a form that mortal men find alluring. Even in its 'natural' state, a succubus draws upon and manipulates mortal men's lusts. They have no choice but to react to the succubus' wiles at +1 CS higher than normal.
Linguistics: succubi make a point of learning a multitude of languages, usually those spoken by the men they prey upon the most. This includes a series of 'real world' languages as well as those prevalent in the planes, as well as the planar trade jargon (English).
Alluring and mysterious, the succubus has a place in many myths for a reason. But do not ever forget that they are demonic entities from the Abyss, and have no goal other than draining the energies of mortals to feed their home - or adding to the countless tanar'ri slaves housed there.
In their 'natural' form, the succubus resembles a tall (six feet) human female, at least superficially. Detracting from this somewhat is the rather large, bat-like wings that sprout out from their backs, as well as their visibly glowing eyes (in a variety of colors).
Succubi are primarily independent operators, acting outside the direct conflict of the Blood War. They are allowed this partial autonomy because their actions bring fresh meat to the Abyss (in the form of abductions), or mysterious power (in the form of their energy drain).
It is not known exactly how the Abyss in general, and the tanar'ri in particular benefit from their vampiric activity, but the tanar'ri believe that both activities are worth the effort. This is why a succubus has a chance (however slim) of summoning balors in the event of an emergency.
Succubi are formed either when weaker tanar'ri ascend to this 'station', or are sometimes the product of tanar'ri breeding; while succubi themselves do not generate more of their kind directly, a mismatched breeding pair (of more powerful and weaker tanar'ri) can result in one.
And that's when a succubus doesn't just spontaneously manifest in the Abyss. This becomes increasingly rare the more powerful a given tanar'ri is, but can happen now and then; on a plane of distilled madness and raging hatred, causality is often a casualty.
Similar to the succubus, an incubus performs the exact same mission, but is male instead of female. It is unknown if incubi cause mortals to give birth to alu-fiends due to their intermingling or cambion, but this rarely comes up enough to be a question.
What with the incubi usually consuming the life force of those they target outside the Abyss.
Either way, the incubus is a much more uncommon creature than the succubi, though it is not known why this is the case. Some sages of the male chauvinist bent assume this is because men are more 'loose' with their passions than women, but the true reason is a mystery as of yet.
* Depending on which version of the Planescape lore you wish to use, the succubi (along with the rest of the tanar'ri) may not have access to this power any longer, having lost it due to yugoloth meddling. Its presence is at the discretion of the individual Judge.