Yochlol, the Handmaidens of Lolth, are tanar'ri. These modified demonic beings from the Abyss possess powerful supernatural powers, both due to their demonic nature as well as due to their patronage to Lolth, and even have a few 'bonus' psionic abilities as well.
Tanar'ri Physique: yochlol are tanar'ri, albeit tanar'ri modified in some dread fashion by Lolth after dedicating themselves to her service. Though this service gives them additional abilities, they still possess the standard tanar'ric abilities, as follows:
* 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 rank value 4, but basically 'blacks out' the sector a yochlol currently occupies (it works within Near range).
* Damage Reduction / Cold, Magical, and Physical Attack: yochlol are incredibly tough creatures. They possess 2 RS of damage reduction against all physical and magical attacks, as well as cold assaults - this on top of their normal invulnerabilities.
* Dimensional Transit: in addition to being able to teleport, tanar'ri can transition themselves between planes of existence. They may do so with rank value 10 ability, though on a failed ACT 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 rank value 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, yochlol 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 yochlol can spy them with ease, doing so with rank value 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 with rank value 6 ability, 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 rank value 30 ability, and can avoid teleportation's usual side effects while transporting themselves within the same plane of existence. *
Bands: yochlol may use this spell-like power to issue forth bindings that are web-like in appearance - but much stronger. They work with rank value 10 ability, easily trapping most conventional opponents, and last for the duration of an encounter.
Charm: yochlol 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 Willpower ACT roll against this rank value 20 power, until it attacks or they can break free of it.
Clinging: yochlol are particularly adept at traversing vertical surfaces. They may do this with rank value 30 ability, meaning they only have problems with intentionally slick surfaces. In their spider form, they may even move along webs with no penalty!
Fangs (spider form): used mostly to deliver their deadly poison, a yochlol can also inflict serious damage with their 'fangs' while in their spider shape. These sharp implements allow the yochlol to inflict their Brawn value in Slashing damage with their mouths!
Poison (spider form): while moving about as a man-sized spider, a yochlol benefits from incredibly virulent poison. Upon inflicting any damage with their bite, a yochlol will instantly inflict a Kill result upon their foes, also inflicting rank value 10 Metabolic damage.
Shape Change: the yochlol are consummate shape shifters. In addition to their default, amorphous state, a yochlol may assume three additional forms: humanoid (a human or drow female), a giant spider, or a dread mist. They can shift forms with rank value 20 ability.
Solid Animation: yochlol have a limited form of this power, which allows them to alter the shape of any object made out of stone (in its natural form or crafted). They may wield this power at rank value 6 ability, usually only on objects within their own, current sector.
Tentacles (slime form): in their natural state, a yochlol possesses eight whip-like tentacles. It may strike with each of these to inflict their Brawn value -1 RS in Slashing damage - but may attempt three attacks with them in a single turn if it wishes.
Transformation / Self: when they transform into mist, the yochlol gain an additional 2 RS of damage reduction against physical and energy attacks, and can move through any opening, no matter how small. However, they're especially vulnerable to air / wind attacks (+2 RS damage).
Natural Psionics (Psipathic):
Psychic Invisibility (a): yochlol can confuse and befuddle the senses of others, making them believe that the yochlol is not, in fact, there. Detecting a yochlol while this power is active requires passing a Willpower ACT against rank value 20 first.
Psychic Probe (a): the yochlol are adept at extracting information directly from the minds of their targets. They wield this power at rank value 10, and can use it to plumb the depths of other people's minds in order to get the dark of what they're looking for.
Mind Control (t): finally, complementing their natural charm powers, a yochlol also has the ability to directly control any one person at a time. They can do this if their would-be puppet fails a Willpower ACT against this rank value 10 psionic.
Limitations / Enhancements:
Susceptibility: like all tanar'ri, yochlol 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.
Personal Weapons: the yochlol usually carry a personal weapon with them at all times, though only their humanoid form can use it. These may include javelins, short swords or hand crossbows - which inflict Slashing, Slashing, and Piercing damage, respectively.
Theology: yochlol not only know the myths and legends of their patron deity, they live them out on a daily basis. They should receive a +1 RS bonus on any Intellect ACT required involving the knowledge of Lolth, her priesthood, her followers, and her many activities on the planes.
For menacing demons of great power and influence, the yochlol work together amazingly well. Fiends through and through, this is most likely out of fear of their patron instead of any loyalty or devotion to Lolth, but one never knows what truly motivates a tanar'ri.
Even one with so close a working relationship with a goddess.
In their 'natural' form, the yochlol appears to be a lumpy heap of amorphous slime. This oozing mound possesses a singular, glaring red eye, and eight whip-thin tentacles with which to assault any number of targets in its area. But the yochlol usually shape shifts outside the Abyss.
They can assume the form of a beautiful young human or drow woman, a human-sized black spider with an incredibly lethal bite, and a bank of dread, demonic mist, depending on their current needs and whatever mission they are on at the time.
The yochlol are not 'natural' tanar'ri, if ever there was such a thing. They are hand-picked by the drow goddess Lolth to further her ends in the Abyss, and infused with power that transforms them into their current state. They do not occur via breeding nor by tanar'ri evolution.
They are most often found on the 66th layer of the Abyss, where their dread mistress rules without question. However, they sometimes journey across the planes on some errand or another, depending on the needs of Lolth. They exist only to serve her and her aims, doing little else.
Divorced from 'normal' tanar'ri culture, the yochlol do not participate in the Blood War unless Lolth specifically wishes it (possibly as a 'reward' for failure). Most other tanar'ri don't bother with them due to fear of their powerful patron, but this is never a sure bet.
Tanar'ri exist to buck authority, after all.
* Depending on which version of the Planescape lore you wish to use, the yochlol (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 Gamemaster.