From publisher blurb:
Better the Devil You Know…
Inspired by Dante’s Inferno, Milton’s Paradise Lost, Junji Ito’s horror manga, and popular monsters of Internet legend, this bestiary features 75 fiends drawn from the Nine Circles of Infernus, including 3 from the dark woods leading to the entrance of Infernus, 4 from the Infernal Vestibule, 3 from wild Limbus, 11 from lustful Salax, 11 from gluttonous Golos, 6 from greedy Avarus, 4 from the wrathful Styx, 4 from heretical city of Dis on Retic, 7 from bloody Phlegethos, 8 from the tortures of the Malebolges, and 2 from treacherous Cocytos. The fiends range from challenge 1/4 (Painfish) to 22 (Dagon, Death, and Milcom).
In addition to the creatures populating each circle, the infernal hierarchy is further divided amongst its nobility: 6 Margraves, 9 Earls, 2 Viscounts, and 1 Baron. Each of the nobles has legendary and lair actions and regional effects.
Don't go into the infernal realms unaware. Know your fiends before they get to know you first!