So they just gave the title and showed the cover mock-ups; no specific info till Monday?
Discover the truth about the great conflicts of the D&D multiverse in this supplement for the world's greatest roleplaying game.
Tomb is a typo. The video will get archived soon.
It was the wrong mockup, wonder what the real one looks like.
Also, this sounds like a DM-only monster manual expansion, rather than a setting book or player-usable book like Volo's.