When did Karsus's Folly become a canon part of the FR lore?

Question

In a recent discussion following the question about edition transitions in the Forgotten Realms, the exact point when Karsus's Fall became part of the canon of FR lore was debated. When the Arcane Age was introduced in 1996, there was the boxed set Netheril: Empire of Magic, which detailed Karsus's Fall and how that caused Mystryl to reincarnate herself as Mystra, and there was also an adventure named How the Mighty Are Fallen, in which the player characters could participate in the final days of Netheril. However the adventure as it was written did not really give the opportunity for the characters to stop Karsus.

On the other hand, it might still be possible to argue that the whole Arcane Age scenario was an optional component, and the DM could entertain the possibilty of having her players stop Karsus, or even claim that Netheril was not even the way described in the boxed set. It could be that Karsus's Fall arc was not really canon; until it appeared in the many 3e products, like the Grand History of the Realms.

So my question is: when did Karsus's Fall become a canon part of FR lore? The question is mainly about which edition of the game, but more detailed data, or some sort of in-game information are also welcome.

Answer 1

I think the Arcane Age and Karsus's Fall entered canon sometime around 1995-1996.

Karsus was described as a "lesser-known" deity in a half-page article by Eric Boyd published in the February 1995 issue (#104) of the Polyhedron magazine. At this point, Karsus is not a dead power and his demise (from greater deity to demigod) was attributed to his poisoning by a Netherese mage named Wulgreth, who sought to steal immortality from Karsus (ironic, isn't it?). So we can conclude that early 1995, Karsus's story as we know it was not yet canon.

TSR released the Netheril: Empire of Magic (N:EoM) boxed set in November 1996. Yet we can argue that Netheril storyline was already entering the FR canon before N:EoM's publication based on evidence from the sourcebook Faiths and Avatars (F&A), which was published in March of that year. F&A has plenty of information about Mystra that foretells the then-upcoming Arcane Age storyline: Mystryl is given as one of Mystra's aliases; her speciality priests can also be of the CN alignment (Mystrl was CN); one of Mystra's symbols is none other than Mystrl's symbol, a single blue-white star. It is worth noting that one of the authors of F&A was Eric Boyd.

Powers and Pantheons (P&P), a companion to and continuation of F&A, was published in 1997. At this point it is clear that the whole Karsus story is canon: P&P lists Karsus as a dead demigod, describing explicitly the events in the earlier Netheril material; including his 12th level spell, and how he used it to steal Mystrl's power and ended up dead.

1998 saw the expansion of the Arcane Age material further with the publication of Cormanthyr: Empire of Elves. This product is also in full support of the Karsus's Fall story, including all the events in the earlier Arcane Age material.

The conclusion is that Karsus's Fall became canon during the 2e of AD&D.

Answer 2

Karsus is mentioned in The Savage Frontier, which was published in 1988.

Karse fell into ruin around the same time as Hellgate Keep was occupied by demons, when the death of the evil wizard Wulgreth caused the creation of the Dire Wood. The wizard yet lives on as an intensely evil, lich-like being within the black pyramid. He seeks pure blood from the heart of Karsus to return to true life. An avatar (minor physical manifestation) of the dying god Karsus dwells in a temple atop the butte, his everflowing blood contributing to the magical nature of the Dire Wood, while deep within the butte, Karsus's gigantic, living heart beats ponderously.

He is not, however, mentioned in the Forgotten Realms Box Set, published in 1987, and which includes an encyclopedia of the campaign setting- it's safe to say he was not canon before that date.

As to when his folly became canon, the Netheril box set is the earliest I've seen so far.