Right, now I've had a fluff-piece to illustrate what these guys are about bubbling away in my head for a few days; but we'll save that for when there's a few more Pishachas ready to put on the painting table.
In the interim, a brief word on the design-choices which went into the character, the miniature, and the unit.
We'll start with the names. For those of you who aren't particularly well-versed with Hindu mythology, "Bhairava" translates as "Terrifying" - and is an epithet of a particularly wrathful aspect of Shiva sent, in part, to deliver justice in an appropriately messy, fiery way. Sound like a Night Lord?
Now as for the rank of "Kapalika" - this translates as "skull-man". I'm reinterpreting it slightly to mean "head-man" (although given this chap's skull-helmet, and the fact he's presumably the best skull-taker in the formation, it's not too much of a stretch); although its main significance for this character derives from something else tied to the real-world Kapalikas
You see, the initial idea behind becoming a Kapalika was that it was a criminal sentence - if you (inadvertently) killed a Brahmin, you were condemned to a period of twelve years as a penitent ascetic ... bearing as an insignia of office (inter alia) a staff known as a "Khatvanga", topped with the skull of the Brahmin whom the Kapalika had killed. (I'll probably flesh out exactly whose skull tops this chap's staff at a later date with someone interesting for fluff purposes).
The reason why the plastic chaplain's crozius was chosen to form a weapon - and a focal point of this miniature, if I do say so - was because all the little skulls running down its shaft put me in the mind of this fine Khatvanga:

There was also one other iconographic element which, while it wasn't necessarily part of the initial conceptualization stages, definitely came to the fore again when looking at the cataphractii librarian miniature. The garland of skulls - a Mundamala - which are suspended about the librarian's chest (somewhat lower down now, given the rebuild which has placed his neck at least half a centimeter higher). A nice tying together of the symbolism of the miniature and its cultural borrowings
Now as for the unit-name - the Pishachas - this has a similar sourcing. They're one of the many classes of demonic spirits or creatures in Hindu mythology; often depicted as being of a dark colouration, with red eyes, and prominent veins running across them. I'm choosing to reinterpret this slightly as being a dark *blue*, glowing red eyes as the lenses of power armour, and with the veins referring to the lightning which often runs across the armour of the VIIIth. In terms of characteristics and abilities, they're often described as being able to move stealthily and to be able to inflict mental disorder upon their foes. Sound like Night Lords?
There's also a troop of them forming a part of the retinue of Shiva, which was partially where the idea for the term as a formation-name for group of warriors around a powerful leader came from.
As for *why* I decided to go down this particular route - rather than the more conventional Greco-Roman (or, as applies Night Lords, Batman) reference-points ... part of it's for personal reasons; and also because I feel that the Dharmic milieus represent a rich and comparatively untapped source of inspiration. But the initial reasoning was actually due to Graham McNeill's The Outcast Dead (one of my favourite of the Heresy novels, for a number of reasons) - and I'm not simply talking about his use of Bengali names for the World Eaters contingent (seriously, given the beatific and calm nature of Rabindranath Tagore, McNeill's use of Tagore's surname for a Nails-ridden XIIth must have been a deliberate stroke of irony).
Instead, I'm referring to the Thunder Warriors contingent and some other details connected with early Imperial power. The ranks which the Thunder Warriors use (Subadar and Jemadar, if I recall) are Mughal military ranks (which were, incidentally, kept in use with the native forces of the British Raj, and other forces of the area subsequent); and some pass which Babu Dhakal is mentioned as allegedly carving out with his bare hands is also on the Subcontinent. This, in conjunction with the fact that the Emperor chose to build his great fortress-prison and stronghold in the Himalayas (which we can feasibly assume was something which transpired pre-Unity, so as to provide a facility to hold those warlords conquered during Unity's bloody process), would appear to suggest rather strongly that the Imperium's beginnings can actually be traced back to this area (particularly given we know the Achaemenid Empire immediately to its west decided to surrender towards the outset of the process, indicating that the wars of Unity must have begun somewhere not too far removed from it).
Now why does this matter?
Well, I'm picturing the Pishachas as being a force of *Terran* legionnaires - much like my IVth Legion; and in a way similar to how other Terran legionary forces seem to have adopted the names and culture of the regions they were taken from, my backstory for this formation of VIIIth is that they're doing much the same (except where the Terran XVth appear to often have had pseudo-Persian affectations - something shared somewhat with the pre-Perturabo IVth; and the Terran IIIrd have gone for the whole European Noble thing; while the Terran XIVth appear to be resolutely British [I particularly enjoyed the British accent which Kage gave them in Turpere Et Dicere]) - and because they're a formation from the later Unification Wars recruited out of somewhere near the Imperial heartlands, their 'origin culture' that they're expressing is North Indian.
(I think I worked out all of the above for my Iron Warriors - and now I suspect I've pre-emptively aired a bit of the surprise that was going to come in their accompanying fluff-piece. Oh well.)
Anyway, now that you've made it through all that ... have some pictures for a scale-comparison.


As you can see, he absolutely TOWERS over a regular, unaugmented human (the Sigillite Emissary from my Agents of the Sigillite warband); and also has a good portion of a head more height than even other truescale Marines (shown next to one of my VIth Legion Huscarla from the same Sigillite warband; and one of my IVth Legion in the mask) - it might not look like the latter, but consider that he's effectively bending backwards on quite an angle, and the size-difference quite quickly becomes apparent.
Vox Stellarum efforts:
The Unyielding Adamanticores [truescale Astartes, auxilia, and sectorial AdMech; M37/38]
The Haunting Harii of Hvergelmir [truescale Astartes ... and associates]
The Unification Wars [truescale Thunder Warriors, (Proto-)Astartes, Army of Unification, Aegyptian-style Proto-Mechanicus raiders, etc.]
Combat Archaeology [Tomb Raiding for Fun & Prophet]
Horus Heresy [truescale loyalist IVth, VIIIth; Agents of the Sigillite; VIth; and so much more; and Umbral's amazing Traitors]
The Worlds-Wide Webway [(Dark) Eldar, Imperial Inquisition, an a-maze-ing realmweave of fear and wondermeant]
Thorian Inquisition [some rather different Inquisitorial Storm Troopers, true-scale Fire Hawks, Black Dragon, Inquisitor and associates, etc.]
For Whom The Great Bell Tolls Thrice [attempts to put the 'priest' back in 'tech-priest' with more-medieval mechanicus]
InquisiNecronMunda [the log that incepted it all - at least two Inquisitors, truescale Deathwatch, local enforcers, cultists, etc.]