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 (a): all tanar'ri have the ability to share the inherent darkness of their very souls with the world at large. This rudimentary power functions only at intensity 4, but basically 'blacks out' everything within near missile distance of the yochlol.
* Dimensional Transit (i): in addition to being able to teleport, tanar'ri can transition between planes of existence. They may do so with intensity 5 ability, though on a failed action dimensionally transiting tanar'ri may be subject to error, per a failed teleport. *
* Infravision (w): 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 intensity 5 skill.
* Invulnerability to Fire, Electricity, Heat, and Poison (s): 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 (w): 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 intensity 8 ability.
* Resistance to Magical Attack (s): yochlol are incredibly resistant to magic in all its forms, possibly as a result of their service to Lolth. They possess intensity 15 (+3) protection from attempts to meddle with their persons with sorcery.
* Resistance to Cold and Physical Attacks (s): furthermore, yochlol are highly resistant to extremes of cold and physical attack, above and beyond what their Strength should offer. They may shrug off the effects of physical damage as if their Strength was +2 (intensity 8).
* Telepathy (w): 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 intensity 5 skill, enough to get their point across when necessary.
* Teleportation (i): chaotic creatures all, the tanar'ri can bend space itself to their will. All tanar'ri possess the power to teleport with intensity 10 ability, and can avoid teleportation's usual side effects while transporting themselves within the same plane of existence. *
Bands (a): yochlol may use this spell-like power to issue forth bindings that are web-like in appearance - but much stronger. They work with intensity 8 ability, easily trapping most conventional opponents, and last for the duration of an encounter.
Charm (w): 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 succumb to an easy difficulty Charm (willpower) action against this intensity 10 power, until it attacks or they can break free of it.
Clinging (a): yochlol are particularly adept at traversing vertical surfaces. They may do this with intensity 13 skill, 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) (s): 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 Strength +2 in slashing damage with their mouths!
Poison (spider form) (s): 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 inflict intensity 10 poison damage as a contingent attack if they pass an easy Poison (strength) action.
Shape Change (a): 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 intensity 10 skill.
Solid Animation (i): 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 intensity 5, usually only on objects within near missile distance.
Tentacles (slime form) (a): in their natural state, a yochlol possesses eight whip-like tentacles. It may strike with each of these to inflict their Strength +2 in slashing damage - but may bring all eight to bear in a single exchange if it wishes.
Transformation / Self (a): when they transform into mist, the yochlol gain +2 resistance to physical and energy attacks, and can move through any opening, no matter how small. However, they're especially vulnerable to air / wind attacks (+4 damage).
Natural Psionics (Psipathic):
Psychic Invisibility (a) (w): yochlol can confuse and befuddle the senses of others, making them believe that the yochlol is not, in fact, there. If a yochlol passes an easy difficulty Psychic Invisibility (willpower) action with this intensity 10 power, their target won't know they're near.
Psychic Probe (a) (w): the yochlol are adept at extracting information directly from the minds of their targets. They wield this power at intensity 8, and can use it to plumb the depths of other people's minds with an average difficulty Psychic Probe (willpower) action.
Mind Control (t) (w): 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 they pass an easy difficulty Mind Control (willpower) action with this intensity 8 psi power.
Hindrances / Augmentations:
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 Strength +3, Strength +3 and Agility +3 damage, respectively.
Theology (i): yochlol not only know the myths and legends of their patron deity, they live them out on a daily basis. They should receive a reduced difficulty on intellect actions required involving the knowledge of Lolth, her priesthood, her followers, or her many activities on the planes.
Idealist, with a secondary calling of Soldier: the masses of yochlol live to serve Lolth, their goddess and ersatz creator. They do what she asks without question, placing her goals above their own interests, for to do otherwise is to court their disaster and doom.
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 Narrator.