What we're seeing here is, in fact, a fairly detailed description of a long-lost, unpublished D&D adventure by Gary Gygax, The Teeth of Barkash-Nour. Those who've read the AD&D Dungeon Masters Guide will undoubtedly be aware of the Teeth of Dahlver-Nahr in the artifacts section. Presumably they're the same thing (not sure why the name was changed). I've always been intrigued by this description, because the adventure sounds really cool and weird, and not really like any of the D&D adventures TSR published, and like something that would've made a great addition to the canon.
THE TEETH OF
A sad twist to what would otherwise just been an intriguing bit of trivia is that this adventure actually was supposed to be published. Around the same time the Believer profile was published, D&D superfan The Dungeon Delver was actually contracted by Gary to expand Gary's notes from the 70s into a full adventure, which was to have been published as part of the "Castle Zagyg" series - it got cover art and everything. Alas, it was never released, and after Gary's passing his widow canceled the entire Castle Zagyg series and the whole thing has been in limbo ever since, which doesn't appear likely to change anytime soon, if ever.
Dungeon Delver is an online buddy of mine, and I've occasionally pestered him for details about this adventure over the years, and he's obligingly provided a few. Yes, the Teeth of Barkash-Nour in this adventure are the same thing as the Teeth of Dahlver-Nahr in the AD&D DMG. The adventure is set on a strange demiplane, accessed through a Gate of Horn deep within Greyhawk Castle (very similar to both The Isle of the Ape and Dungeonland). The encounters are as mentioned in the article, plus a few more equally-weird and colorful ones that I'm not at liberty to describe. And the manuscript was complete and handed over to Troll Lord Games (Gary's publisher at the time) for final production and release well before the line was canceled. Alas, that never happened, because, as 'Delver tells it (in a story I'd heard privately a while ago, but which he has only just made public) he was submarined by Frank Mentzer, who convinced Gary to halt publication on specious legal grounds in order, apparently, to set himself up as the savior and take credit for "fixing" a product he had nothing to do with the creation of. Sleazy underhanded stuff, and doubly unfortunate since the delay caused by Frank's interference, coming as it did shortly prior to Gary's passing, ended up dooming publication altogether.
There are a lot of intriguing and agonizing could-have-beens in Gary Gygax's career. Heck, I compiled a whole book out of my takes on some of them. But the Teeth of Barkash-Nour are a particularly tantalizing and frustrating example, because this isn't just something Gary talked about maybe writing someday, or some set of minimal, barely-legible notes, or something rumored that may or may not have ever existed in the first place, this is an actual honest-to-goodness complete D&D module that was all-but-ready to go to press, and which is presumably still sitting around somewhere as a complete manuscript. Just like the guys in the article, we came so close to having this thing in our hands.
Maybe it's unrealistic of me, but I still hope that someday maybe Gail Gygax will change her mind and we might still be allowed to see it. But I'm not holding my breath...