In the section of the adventure not yet within Perdition, we get the full statblocks of some named NPCs spread out across the different pages.
In the section of the adventure within Avernus itself, we get the full statblocks of the aforementioned, plus we get Siberiex, named NPCs like a rakhasha entrepeneur named Mahadi who parades around in the Wandering Emporium (where you can get actual food, do you need to pay for that food with your soul?), an eldarin called Smiler the Defiler (that's a freaking excellent name), plus things like the abyssal chicken (tastes like burning chicken all the way down I presume), the abyssal wretch, something called the bone whelk (large slug monstrosities that carry a cage of bones on their backs). It's all definitely extremely metal \m/