The somewhat rare mariliths are powerful Abyssal demons. Considered 'true' members of their race, they possess a vast array of supernatural powers with which to wage the Blood War, and are partially immortal in that even death outside the Abyss may not stop them for long!
Tanar'ri Physique: as true tanar'ri, mariliths are incredibly dangerous demonic entities. They possess a large array of physical and supernatural powers, an inherent psionic potential, and even the ability to shrug off death! Their considerable powers include the following:
* 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 marilith.
* 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. Mariliths in particular possess immunity to fire, electricity, heat, and poison.
* Portal Sense (w): planar beings all, mariliths 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 mariliths can spy them with ease, doing so with intensity 8 ability.
* Resistance to Cold and Physical Attack (s): while they're not immune to the effects of these attack forms, tanar'ri are considerably resistant to such. When exposed to any form of cold or physical attack, a marilith may resist such as if their Strength was +2 higher (intensity 8).
* Resistance to Magical Attack (s): mariliths are incredibly powerful creatures of chaos. They are thus highly resistant to efforts by others to impose their own reality upon them, and as such can resist magical effects and damage at a whopping intensity 21 (+5)!
* 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. *
Additional Limbs / Arms (a): their signature trait, all mariliths possess six arms. This allows them two additional melee attacks every exchange (dividing their pre-cardplay action score between them), each of which are usually made with different weapon types.
Additional Limbs / Tail (a): the lower half of the marilith's body is serpentine. They cannot wield this as a limb delicately, nor can it serve as a battle tail, but it can be used to constrict foes (Grappling attacks) at the marilith's Strength score +2.
Curse (w): this spell-like power allows a marilith, if they pass an easy difficulty Curse (willpower) action against their target, to subject them to a curse. This intensity 12 power normally takes the form of a -1 on all actions, but its nature can vary considerably.
Danger Sense (w): the elite marilith tanar'ri are rarely, if ever, surprised by anything in their environment. They possess this supernatural awareness of their surroundings at intensity 12, which informs them of any dangers, active or passive, that threaten them.
Death Touch (s): a marilith may cause wounds to spontaneously form on touch, inflicting immediate damage. This anti-life power inflicts intensity 12 metabolic damage as a contingent action (after a successful melee attack), on an easy difficulty Death Touch (willpower) action.
Fire Generation (i): completely immune to flames, mariliths may nonetheless generate them to attack their foes - or just to toy with the destructive energy, depending on their whims. They can spontaneously create fire and heat of intensity 12 power.
Imaginary Doubles (i): mariliths have the curious ability to generate an imaginary, pretend double of themselves. This double is immaterial and cannot attack others at all, but the marilith can see through its eyes and hear through its ears. This is an intensity 1 power.
Linguistics (i): while they are inherently telepathic, mariliths often prefer to engage others verbally - particularly when they're shape changed (to keep up the disguise). This intensity 12 mental power allows them to do just that, with any number of different species.
Magic Sense (w): all mariliths have the ability to sense ambient magic in their environment. They may do so with intensity 12 ability, which lets them spot magical items, beings, and other phenomena within far missile distance of their person.
Nonapparent Vision (w): at will, a marilith can activate this sensory capacity in order to see something as it truly is. This intensity 12 ability easily allows them to pierce the veil of disguise, whether physical, mental, spiritual, or otherwise.
Philosophical Sense (w): another of their useful sensory powers, mariliths have the ability to 'feel' the philosophical bent of any person, place or thing they observe. They can sense something's leanings towards order, chaos, good, evil, or balance with intensity 12 skill.
Poison (s): in addition to direct physical damage, mariliths can also inflict an insidious, creeping doom upon their foes. They can apply this intensity 12 power to their very breath, causing it to seep out and reach anyone within near missile distance.
Those who inhale these lethal fumes must pass an easy difficulty Strength (poison) action against this power or suffer like metabolic damage each exchange the marilith continues to exhale them. Assuming the marilith don't just chop up its enemies while they gag on the deadly fumes...!
Reanimation (i): in addition to summoning forth weaker tanar'ri to do their bidding, mariliths can literally create reinforcements - most often from the bodies of fallen foes! They can build zombies or skeletons out of corpses, a skill they wield with intensity 12 ability.
Revival (s): like other true tanar'ri, mariliths can sometimes give death the laugh. Unless killed inside the Abyss or eaten, mariliths may attempt to reconstitute themselves on their home plane with this intensity 5 power. The difficulty involved depends on how they died.
Shape Change (a): up to seven times per day, a marilith may change its shape. This allows them to slip into enemy encampments mostly undetected, or to otherwise enjoy the benefits an ever-changing form provides. They may wield this supernatural power with intensity 12 skill.
Summoning (i): a marilith may summon forth their fellow tanar'ri in great numbers, and quite often. Once per hour, they may attempt to use this intensity 5 power to draw forth their demonic brethren, and they have a wide selection of tanar'ri to choose from, too.
When they successfully activate this ability, mariliths can draw forth from two to twenty least tanar'ri, from one to six lesser tanar'ri, from one to four greater tanar'ri, or another true tanar'ri. This is not random; a marilith may choose the level of support they're summoning.
Telekinesis (i): though they usually prefer direct intervention, a marilith may impose its desire on objects in its vicinity. It may 'only' do so with intensity 10 ability, but this allows the creatures to move 800 pounds of matter just by thinking about it!
In addition to the above, considerable array of supernatural powers, mariliths are also equipped with natural psionic abilities. These capabilities will vary from marilith to marilith, but will usually be of either a metapsi, psikinetic or psipathic bent, most often being destructive in nature.
Hindrances / Augmentations:
Susceptibility: like all tanar'ri, mariliths 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.
Weaponry (s): mariliths usually carry a wide variety of ornate weapons, whether of a melee or ranged persuasion. These function in the normal fashion, though they're often enchanted to offer a +1 to either hit or damage - if not both, depending on the marilith.
Leadership (w): mariliths are natural tacticians. They can easily plan battles around almost any contingency, no matter how bizarre, and anyone following a marilith's plan (good luck with tanar'ri) receive a +1 bonus on pertinent actions while doing so.
World Domination: mariliths rage and murder and destroy with the best of the tanar'ri, but they usually do so for a reason. Their ultimate purpose is to manage the Blood War, in order to spread tanar'ri dominion across the very multiverse itself!
Mariliths feel the same hatred, insanity and rage that other tanar'ri feel, but they have the ability to manage it. This allows them to become keen tacticians, their genius intellect able to focus long enough for them to use anything and everything available to them to their advantage.
They are also quite arrogant, looking down on the 'cowardly' tactics of the glabrezu and even the 'boorish' might of the balors. If they had their way, the mariliths would be running the Blood War. Unfortunately (for them, at least), they are rarely able to assert their proper might.
Mariliths, from the waist up, appear to be beautiful humanoid females, albeit with six arms. From the waist down, they have long, serpentine bodies, which they can use to grapple others like a boa constrictor (though they can't actually club a foe with their lower half).
The elite tanar'ri known as mariliths are the brains behind the chaos side of the Blood War effort. While the balors are the drive and authority behind its persecution, the mariliths are those who make it happen, their keen minds forever forging plans against the hated baatezu.
Skilled warriors and generals, mariliths feel that they are the true force behind the tanar'ri half of the Blood War, and that balors only hold their position due to raw power. Mind you, they rarely act out against their 'betters', unless they have a foolproof plan with which to do so.
A lot of this bile towards balors involves their tolerance of glabrezu. Mariliths hate the sneaky, underhanded activities of the glabrezu, and would wipe them out on sight were they not protected by the balors who adore their tactics. If left unprotected, a glabrezu is easy prey for a marilith.
The mariliths themselves are somewhat uncommon in the Abyss and elsewhere, for it takes a staggering amount of suffering - both given and received - to forge a tanar'ri into this form. Eons upon eons of such is necessary for a tanar'ri to grow into enough power to become a marilith.
This is the only way a marilith comes about. As is the case with other true tanar'ri, mariliths cannot form spontaneously, nor can they be the direct result of breeding between other tanar'ri. Only the endless evils of the Abyss can forge lesser beings into one of these unholy terrors.
While reports of them manifesting abruptly from nothingness in the Abyss occur, the truth is that these are witnessed accounts of mariliths returning to life as a result of their revival power - which usually reforms a defeated marilith's body in their home plane should they die elsewhere.
* Depending on which version of the Planescape lore you wish to use, the mariliths (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.