Deep Dive into Descent Into Avernus
The seeds for Baldur's Gate: Descent Into Avernus were planted in last year's release, Mordenkainen's Tome of Foes (MToF). At the time, D&D Lead Designer Jeremy Crawford described the theme of that book as “conflict” and the chapter on the Blood Wars between devils and demons in the D&D multiverse is the foundation for Descent Into Avernus.
Readers of my first impressions review were concerned that first-level characters would be hopelessly outclassed in the first plane of hell. However, since BG: DIA recommends milestone experience, PCs should be 5th level when they help survivors of Elturel, which has been pulled into the first layer of the lower planes, suspended by chains above the River Styx, then 7th level when they enter Avernus proper, and 13th level or higher when they try to return to Baldur's Gate – assuming they live that long. Even at 7th level, the adventure is a challenge, but they at least have a chance.
While BG: DIA is designed to be self-contained, it would be very wise for DMs to read the Blood Wars section of MToF's. Players can, too, but personally, I'd rather have the DM give the players relevant background material based on what their characters would know. Of special note is the information on Zariel, who was once an angel of Mount Celestia but now rules Avernus, having been corrupted while watching the Blood Wars rage. Impetuous, she eventually dove into battle there with her followers, convinced they could wipe its evil and claim the plane for good. She was wrong. Asmodeus found her unconscious under a pile of her conquests. When she recovered, he gave her dominion over Avernus and named its prior ruler, Bel, her lieutenant. The stats for Zariel in BG: DIA and MToF match, but the later provides a lot of personality information that are useful for DMs. BG: DIA has essential background but it's better to use both.
Before the start of BG: DIA, the city of Elturel has disappeared, pulled into the lower planes. The chaos this causes...