... While reading SF, there's no real indication that anything deeper is happening. It just seems like the Shadowman found some old books and learned some intro black magic and used it to make Three-Eye.
Yet in later books we find out that there's a bigger force moving behind all of this...
This is a recurrent theme of the DF novels: later-series Harry, with more maturity & more power, swimming in deeper waters, has more information and a more-nuanced understanding (than earlier-series Harry). When Harry first introduces her, Mab is "queen of the Evil faeries" and the archetype of all villainous malice. Later, we learn she is on
Team GoodGuy(tm)... just, one of the more cold-blooded members of the team.
Part of the fun of WAG'ing in the fandom is trying to figure out some of that -- spot the easter-eggs, unravel the clues,
beat Harry in achieving that nuance!
Specifically: What is Nemesis' Plan in Storm Front?
... learned some intro black magic and used it to make Three-Eye.
Yet in later books we find out that there's a bigger force moving behind all of this. Assume for the moment that Harry doesn't stop Victor. What does this accomplish for Nemesis' What's their end goal in "helping" the Shadowman here?
Nemesis wants the Outsiders back "inside" Creation; that's the Big-Picture plan.
As to the specifics, I agree with @Talby16... it's this, I think:
Precisely. Nemesis says in Battleground through Justine that apocalypse isn't an event, its a frame of mind. Flooding the streets with the Three Eye Drug would help lay the framework of that frame of mind in the populace.
IIRC (I don't have the PT/BG texts on hand, to ^F thru) Ethniu voiced a similar sentiment. She wanted the mortals aware of magic once again; and cowed by it. Given that Three-Eye let mortals see magic, this is clearly one of the Nemesis/Outsider through-lines.
I think we should take this as part of that "apocalyptic state of mind:" mortals who see the magic -- or at least believe it's there, even if they don't see it -- are expected to be more "apocalyptic."
And indeed, "magical foes, beyond mortal soldiers' ability to kill" looks
very much like something that could prompt the battlefield use (for example) of nuclear weapons / WMD, which is another "apocalyptic" sort of mindset. For those without Maximum Overkill weapons to hand, hopelessness and despair -- and desperate longing to have such weapons -- seem like common reactions to things like the Superghouls in the Raith Deeps, or Ethniu's personal combat prowess, or the realization that Winter comes to anywhere that Mab comes (potentially destroying a year's crops) &c.
"Apocalypse: the Mindset" would seem to follow naturally.