There are theoretically an infinite amount of alu-fiends in the Abyss, but these tanar'ri are somewhat rare. The descendants of demonic succubi and mortal males, the alu-fiends are most often evil entities, and possessed of startling supernatural powers both natural and trained.
Tanar'ri Physique: while they are weaker than most other tanar'ri, alu-fiends are considered 'actual' members of the race. The offspring of tanar'ri succubi and mortal males, alu-fiends are true planar entities, and 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 an alu-fiend currently occupies (it works within Near range).
* Damage Reduction / Cold and Magic Attacks: though not immune to the effects of cold or magic, alu-fiends are considerably resistant to these attack forms. When exposed to any such damage, an alu-fiend may reduce its intensity by 2 CS - before any other defenses apply.
* Dimensional Transit: in addition to being able to teleport, tanar'ri can transition themselves between planes of existence. They may do so with Good (10) ability, though on a failed FEAT roll dimensionally transiting tanar'ri may be subject to error, per a failed teleport. *
* 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, alu-fiends 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 alu-fiends 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. *
Body Armor: supplementing their already impressive supernatural defenses, alu-fiends also possess natural ruggedness. They possess Typical (6) protection against physical attacks, which also offers them Feeble (2) defense against energy-based attack forms.
Charm: alu-fiends 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 Psc (will) FEAT roll against this Excellent (20) ranked power, until she attacks or they can break free of it.
Danger Sense: a powerful gift they inherit from their mothers, alu-fiends are rarely surprised. They possess this supernatural awareness of their environment at Good (10) rank, which informs them of any dangers, active or passive, that threaten them.
Disguise: this Typical (6) power allows the alu-fiend to superficially change their appearance. They may assume the form of any humanoid being, regardless of gender or other qualities, as long as they remain the same approximate size (no size change greater than 50 percent).
Flight: alu-fiends have small, bat-like wings issuing forth from their back. Only a foot or so long, these seemingly useless appendages are nonetheless imbued with the magical power of flight, which alu-fiends can use with Poor (4) ability (60 MPH).
Mesmerism: alu-fiends 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 Good (10) ranked power or comply. Of course, obviously harmful instructions automatically fail.
Portal: in addition to the normal tanar'ri ability to teleport, alu-fiends wield the power to build a momentary portal between one location and another once per day. This skill works with Remarkable (30) strength, but functions on the Near range table (8 area range).
Vampirism: while they possess no inherent physical weaponry like most tanar'ri, alu-fiends have the ability to drain energy from those they touch. This power works at Typical (6) rank, but life drained can only be used to restore lost Health points.
Philosophical Magic: a small number of alu-fiends possess actual education in sorcery. These typically have a Reason score above the Good (10) rank listed above, and will be from novice to disciple level in this school (from one to eight spells).
Alu-fiends most often wield the power of Destruction, a blending of Chaos and Evil, but occasionally lean towards one or the other of those core philosophical forces instead. Very rare alu-fiends will wield philosophical magics of Corruption, Disruption or even Balance.
Limitations / Enhancements:
Susceptibility: like all tanar'ri, alu-fiends 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 an alu-fiend's maximum Health in damage.
Magic Items: alu-fiends usually carry at least one magical item, a gift (or gifts) from their mothers. These are most often low-level magical items, providing a +1 CS to hit and/or +1 CS to damage (weapons), or +1 CS to their Body Armor and/or even 1 CS of deflection (armors).
Attractive: alu-fiends have a certain something about them that people seem to find attractive. Unless they exhibit the conventional tanar'ri behavior (mindless bedlam and violence), they'll usually receive a +1 CS on NPC reaction from those they interact with.
Lore: whether or not they embrace magic as a supplement to their own power, alu-fiends are all possessed of dark knowledge. Their mothers often give them great secrets and insights into the tanar'ri and the Abyss, and their Reason should be considered +1 CS in such areas.
Weapon Skill: similarly, alu-fiends will also train rigorously in at least one weapon, even if they have sorcery to lean on. This will most often be an education in the use of whatever magical weapon(s) they possess, which they'll be able to use at the applicable ability +1 CS.
Alu-fiends are all rather hateful. Feeling outcast from both human and tanar'ri society, the alu-fiends rage against all who would belittle them, and avenge all slights real and imagined when possible. A rare few alu-fiends are a little less extreme in their behavior.
Alu-fiends appear, on a first glance, as perfectly normal human females. A closer inspection however will reveal their seemingly 'powerful' features, along with conspicuously up-sloping eyebrows, not to mention the small, supernaturally powerful bat-like wings on their backs.
The alu-fiends are low on the tanar'ri totem pole, and most tanar'ri look upon them with disdain since they did not earn their power; alu-fiends only come about as the children of succubi. Of course an alu-fiend, like all tanar'ri, can earn the respect of its kind with raw power.
* Depending on which version of the Planescape lore you wish to use, the alu-fiends (along with the rest of the tanar'ri) may not have access to these powers any longer, having lost them due to yugoloth meddling. Their presence is at the discretion of the individual Judge.