Mordenkainen Presents: Monsters of the Multiverse is now available to buy, a day earlier than scheduled. While it releases most places tomorrow, you can grab it from D&D Beyond today.
dnd.wizards.com

Monsters of the Multiverse | Dungeons & Dragons
Discover a multiverse of lore with over 250 monsters, combined and updated from Volo's Guide to Monsters and Mordenkainen’s Tome of Foes.