Hmm. Six new stat blocks, possibly seven depending on whether Zariel's stats are the same here as is MTOF, but no additional Archdevil stat blocks. Bel was originally defined as a Pit Fiend, and I'd expect he has lost the power boost that drawing off of Zariel gave him, so presumably standard Pit Fiend stats could represent him (I hope he appears in the adventure as he was a former Lord of the Nine and might be again, perhaps, if Zariel leaves. If he doesn't wind up in charge again, I'm at a loss as to who it'll be.) Somewhat disappointed that there are no new Archdevil stats but writing an adventure where they could all be used would be a challenge. The new material covering Avernus will be useful as - let's face it - that's about as far as most adventurers are going to get into the Nine Hells... nice touch that they mentioned Gargoth, the "lost Lord of the Nine" in Forgotten Realms material... maybe HE takes over? Also, there are a lot of outcast Devils on the First Layer, and the PCs might encounter them (many are quite interesting) if the DM wants to include them. Not necessarily in this specific adventure, but at some point, given all the material provided about Avernus - why only have the PCs visit once? Not everything I was hoping for, but certainly sounds worth the purchase.