Lost my originals three computers ago, and anyway the server's changed a lot since then. So.
I'll be working through Drow of the Underdark first.
Arachnomancer
"By discarding the religious traditions dominating drow culture, the arachnomancer finds a different way to serve the Weaver of Webs. Through careful study, the arachnomancer comes to understand spiders in a unique and disturbing way, developing a rapport with the vermin. It doesn't take long for the arachnomancer to shape his magical studies to awaken the Spider Queen's blessings within himself, allowing him to assume the form of a monstrous spider."
Entry Requirements
Any Evil
Climb 4, Knowledge Nature 4, Knowledge Religion 8
Feat: Verminfriend
Spells: Ability to cast spider climb, summon swarm, or web as an arcane spell.
Class features, with Arelith substitutions:
Spellcasting: Simple. No way to run this without a caster class. Interestingly, the sourcebook claims that only arcanists can become arachnomancers, but sweet mercy how horrible would that be. We're running this as ONE OF: an NE spider totem druid of Toril, who through some spiritual jumprope believes that serving spiders and the caves that they live in somehow serves Lloth, OR: A wizard/sorc with a real affinity for polymorph self. OR: A semi-heretical cleric of Lloth with the plant and animal domains. (Animal grants polymorph self)
Poison Save Bonus: Well, druids gain immunity. Real nice in the UD. If you really want to get a spider-venom-y vibe, though, roll 3 or so levels of assassin into it for poison use. Poison's as natural to the UD as, well, mushrooms. Note: The arcanist version will absolutely want this. It's just nice flavor for the druid.
Handle Spiders: What is essentially a spider-only bonus to animal empathy. Sadly I... don't believe spiders are empathy-able here? Something about mind spell immunity? Is that snakes? Anyway, the arcanist is going to want, somewhere in there, ranger or druid levels if it IS possible. (A couple druid levels for a spider companion would not be amiss, really.)
Spider Domain: Mostly, this gives you powers like webs, spider summons, and the ability to rebuke vermin. Not much of a thing in NWN, not really.
Spider Shape: Pretty much the big one. This is where druid really shines versus the others, since their spider shape is combat ready, rather than just for aesthetics.
Tremorsense: I guess high listen ranks can imitate this.
Webwalking: The ability to ignore web effects. Or: Something druids can do innately. Really, no matter what you're running (cleric or arcanist) you'll probably want a Couple druid levels in there.
Climb Speed: is this a thing here? no? later.
Playing an Arachnomancer wrote:"You are obsessed with spiders. They fill your dreams and your waking thoughts. The extent of your preoccupation does not stop with ordinary spiders. You are fascinated by all spiderkind, from the monstrous spiders of the Underdark to the dreaded bebiliths that the priestesses conjure for th emost profane rituals.
Even when not studying spiders, you find ways to bring them up in conversation, dropping fascinating (to you) tidbits and trivia about different breeds of spiders, their mating habits, and their hunting habits, and going to great lengths to extol the virtues of the vermin. Although the drow might tolerate or even appreciate such insights, your attraction to spiders does little to endear you to members of other races."
In Summary: So in PnP the Arachnomancer class serves, basically, as a way for drow arcanists (who are stereotypically male) to interact more fully with the 'drow ideal' of a crazed spiderkisser. They're semi-heretical in the way that everything that isn't the 3 generic drow archetypes Salvatore presented is, but serve an interesting purpose as basically hyper-nerdy spider tenders, which is apparently a necessary enough role in drow society that there's a class about it.
On Arelith, the best way to run this is with a studious totem druid who does some semi-heretical mental gymnastics (so, a drow) to justify their behavior. Like, it's really just the druid class with a spider bent, an evil restriction, and dedicated to a non-druidic god. (Although the argument could theoretically be made that a deity of vermin sort of counts as a druid god, maybe.) It's
doable as a wizard or sorc with some messy multiclassing, but your mileage may vary, etc.