Devil (Archdevil), Moloch
A traitorous servant of Baalzebul, Moloch is a CR 26 archdevil that schemes to rule the sixth plane of Hell after he managed to get rid of Geryon and his bloated boss. He is pretty much another standard archdevil, with his spellcasting being that of a 20th-level Cleric, his prerequisite fear delivery being through a breath weapon, and his unique melee weapon of choice being a +4 unholy shocking six-tailed whip. I can't really recommend using him over any other archdevil unless you have parties that are weak against electricity and you want to be a jerk toward them or you want to explore the sixth level of Hell in particular. Moloch has no real particular favorite type of servant beyond "humanoids" (wow, that's a small category right there) that are wizards, clerics, or assassins; such individuals that sign a pact with the archdevil are known as Knights of Moloch.
These devils are literally lemures that were born wrong. Yeah, I'll let that sink in for a moment.
...Okay, sinking time's over. As a result of their origin, nupperibos are some of the absolute weakest, "kick me"-signed devils out there at a pathetic CR 1. They are worthless as anything but cannon fodder due to the fact that they are mindless and have nothing but their nearly worthless regeneration 1, minor damage reduction, and average acid and cold resistance to keep them alive in combat. The only reasons I can see for using nupperibos are for their flavor (nupperibos as a concept are admittedly rather creepy, and it's even worse when you realize that even if a nupperibo gets promoted (a listed 1% chance), its reward is...to become a lemure. Some reward, that) or if you want to introduce devil hordes really early in your game.
Devil (Duke), Titivilus
Unlike most dukes, the CR 20 Titivilus commands no specific type of demon, although he does have some erinyes and bearded devils that hang out under his watch. He is the messenger of the archdevil Dispater and is pretty average as far as the Dukes of Hell go, right down to his archetypical goat-and-bat features. He has generic Duke powers as well, with his prerequisite fear ability being fear touch and his unique weapon being a +3 wounding silver longsword. Meh.
The tormentor devils prowl the uppermost plane of Hell in search of escaped souls, hell hounds in tow, hunting them down to bring back to whatever archdevil has hired them; and with a name like "tormentor devil", you just know they're gonna treat your soul right. Anyway, they are CR 7 and have a lot of soul-hunting specialties. Their natural weapons are treated as having the ghost touch special quality, as are their +1 battleaxes and barbed nets, allowing them to damage and capture souls with maximum prejudice. In addition, they can track souls as if they were living things, which makes me wonder why they even have the hell hounds if they can do the tracking on their own...symbolism, maybe? I dunno. In any case, the tormentor devil is a nasty little surprise for any would-be rescuer of the damned that starts their descent into the depths of the Nine Hells.
And that's it for the devils.
...Wow. I hadn't even thought of what I'd say at this point. We've done it; we've actually reached the apex of this Let's Read. The Tome of Horrors has been read in its entirety now! It was one wild ride, and I'm glad I was able to take y'all with me on it. It may have had its ups and downs, but the ToH is still one of my favorite monster books, and reading it from start to finish for this thread really cemented that in my mind. So once again, to all you ladies and gents that followed this thread, thank you...
...Oh, and the next Let's Read won't be the Tome of Horrors II. No, two Tomes in a row would be silly. So tonight (or tomorrow morning, not sure), we'll be venturing to another WotC-licensed third party bestiary. One that comes from a truly dreadful place...best bring your lanterns, because it's gonna be dark out there this October.