So I guess this is a thing for sale now?

https://www.dndbeyond.com/marketplace/sourcebooks/adventure-atlas-the-mortuary

It says it comes with some stuff:

This creepy location can fit into any game and be explored in any campaign! Explore the Mortuary, the otherworldly and infamous home of the mysterious Heralds of Dust. Discover new lore, fierce monsters, dangerous encounters and detailed maps to give Dungeon Masters everything they need to weave their own stories:

• Add 3 new monsters that are usable in D&D Beyond DM tools like Maps & Encounters
• Unlock 5 new maps optimized for the Maps tool
• 4 climactic encounters for player levels 3-11
• Droppable location for any adventures or campaign
• Detailed lore, faction information & locations within the Mortuary

This purchase unlocks the contents of this adventure for use with D&D Beyond, including the book in digital format in the game compendium and access options from the book in the searchable listings, Encounters tool, Maps tool, and digital character sheet.

By chance does anyone know what the two monsters besides the Animated Coffin are? I can't seem to find a list and I also can't seem to purchase those monsters piecemeal outside of the adventure proper? I also am not sure of the two mystery monsters are worth it to me at the moment for having to also buy an adventure I probably don't need.

It was posted the same day Planescape released. The other monsters are:

• Factol Skall (CR 17)
• Heralds of Dust Exorcist (CR 6)

And there's also reprints of:

• Necrichor (CR 7 - originally from Van Richten's)
• Planar Incarnate (CR 22 - originally from Planescape)

So for anyone who doesn't own those, it is actually 4-5 monsters.

And it's not even really an adventure, it's quite a bit more lore on the Heralds of Dust, and details on various adventure locations in the Mortuary (5 locations with maps & descriptions for Tiers 1-3, encounter tables for Tiers 1-3).

I've purchased the new, physical, Planescape boxed set from Amazon. Now I purchased "Adventure Atlas: The Mortuary" here. How do I view that content?

At the top of this page go to the "sources" tab.  That will give you a drop down menu on the left "sources" menu, you'll see Adventure Atlas: the Mortuary on the left.  Click it takes you to the product.

Thanks!