I’d like to design the archetypal Ahrimanic villain character as a composite of the following:
-The Witch King and his posse: the Ringwraiths (LoTR)
-Pinhead and his posse: the Cenobites (Hellraiser)
-Void and his posse: the God Hand (Berserk)
-The Red Sphinx (Dumas)
-Faust (the man, not the Satan character)
-Legato and his posse: the Gung-Ho Guns (Trigun)
-IT (the shapeshifting spider alien demon from the book)
-Posse only: the Black Hand of the Dark Brotherhood (Elder Scrolls)
-Superhuman planning ability
-Drives the story
-Serves Lucifer directly, an angelic, god-like superman (e.g. Knives)
-Therefore not the final boss, but is the final monster you actually see and fight (whereas you don’t actually see or fight Sauron, Knives, or the final Norn guy in Memory, Sorrow, and Thorn)
-Master of horror
-Local reign of terror from a big, dark prison tower dedicated to torture (e.g. Bastille)
-Always brings dark posse (e.g. Ringwraiths, )
-Black leather overcoats (black robes are acceptable but that ruins the S&M vibe and makes it more of a basic bitch Satanic witchcraft thing, and being sacrificed in a rite by teenage girls smoking weed is less terrifying than lifelong imprisonment in a big dark torture tower designed to destroy your psyche <- Babel tie-in?)
-Spider-like powers (e.g. Pinhead’s fish hooks, Void’s “threads of causality”, Legato’s metal strings)
-Head shaped like upside-down pyramid (e.g. Void, spider melonheads, Boskop man)
-Feeling of absolute horror that there’s absolutely no escaping once this guy shows up, and worse things than you can imagine are about to start happening and keep happening forever (hence “Hellraiser”, this guy is a herald of your personal Hell)
Unlike Pinhead and Void in Berserk, I think the most archetypal dark posse has nine members so that you can have four on each side and the leader in the middle, representing the arms and face of a spider that’s got you (the fly) in its clutches. Think of the Cenobite scenes where there are chains hanging all over the place and the Cenobites slowly coming from all sides with Pinhead in the middle to get the idea, except imagine there are four on each side like spider arms.
His only weakness, as mentioned in the Alchemist post, is that he’ll make errors on purpose in order to feel the passions of youth again (see Faust, Hellraiser 2: Hellbound). So if you were to offer him the possibility of being seduced, being the passive protagonist in a story designed by you to stir his emotions, he would be literally unable to not choose it. This could be expressed in a very basic character as him having a serious weakness for rail shooter games. Literally unable to do anything but react.
This character is sometimes done as a female, e.g. Salem in RWBY https://rwby.fandom.com, Utuk’ku in Osten Ard stories, but I don’t feel it carries the same weight of terror or realism. There’s definitely a place for a Shelob type of character in fiction, just not as an Ahriman stand-in. Girl spiders are more like a morality tale about staying away from psycho bitches. The Osten Ard stories kind of pull it off by splitting it into Pryrates, the red priest, and Utuk’ku. Notably, the name “Utuk’ku” comes from a very God-hand-like class of demons (utukku) in Akkadian mythology: https://en.wikipedia.org/wiki/Udug.