We've already guessed the upcoming streaming event / campaign book announcement relates to beholders, Xanathar, and Waterdeep/Undermountain. And it's been noted that the tagline "No Stone Unturned," found both in the event announcement and the currently-ongoing "alternate reality game" is a reference to the old video game Eye of the Beholder, in which "Leave No Stone Unturned" is found carved on the wall of Xanathar's outer sanctum.
But there's more. This morning, reading through an old D&D supplement, I stumbled upon something I haven't seen mentioned anywhere yet.
It turns out "Many Eyes" is actually a specific entity in Forgotten Realms lore -- and he lies the origin of a powerful artifact called the Eye of the Beholder (apparently unrelated, until now, to the video game of the same name).
This is a from the 2e supplement Volo's Guide to All Things Magical, by Ed Greenwood and Eric L. Boyd, p. 123 (all italicized emphasis mine):
"In the dim history of the Underdark, the drow city of Menzoberranzan was founded by refugees from the war-torn city of Golothar led by Menzoberra, the high Priestess of Lolth. Following their defeat of the dwarves of the Black Axe Clan, the drow refugees discovered a massive underground cavern called Araurilcaurak ("Great Pillar Cavern"). At the command of their dark goddess, the drow settled the cavern and drove out all the previous inhabitants, including a monstrous beholder known as Many Eyes.
The beast, also known as Yuthla, was a massive beholder rumored to be over 30 feet in diameter with over 100 eyestalks. Drow scholars later theorized that the monster reached its abnormal size due to the high concentrations of Underdark radiation in that region. The scholars believe Many Eyes was a variety of elder orb, given its spellcasting ability and ability to direct scores of undead beholders (also known as death tyrants). After a climactic battle in which hundreds of drow and their slaves were slain, Yuthla was destroyed.
Drow legends relate that immediately following Yuthla's death, Menzoberra plunged her fist within its carapace and withdrew its still-pulsing "inner eye" which served as the beast's brain and heart. In an unholy rite of devotion to Lolth, Menzoberra petrified the organ and encased it in a magical variant of amber. The resulting gemlike stone was magically reduced and mounted on an adamantine torc which Menzoberra wore around her neck until her death.
Menzoberra is believed to have used the artifact, referred to in the old stories as 'Yuthla the Eye of the Beholder,' to aid in the construction of the new city and to clear monsters from the surrounding wilds of the Underdark. Following Menzoberra's death, the inlaid torc disappeared in the subsequent power struggle between her daughters. Although numerous drow matriarchs have searched for the artifact in the intervening centuries, no trace of the Eye has ever been found."
The book goes on to discuss rumors of a (relatively) recent clue to the artifact's whereabouts, then lists the artifact's powers, which include creating and controlling death tyrants; granting its wearer all the powers of a normal beholder's eyes (once a day each); and a 9th-level spell called "tyranteyes" that allows the caster to actually transform indefinitely into a beholder.
