==Moloch, Khan of the horde ==
Moloch is the most powerful and cunning fiend in the abyss. He has coerced the loyalty of more demons than any other and plays the other lord one against the other to stay on top. He dreams of conquering and laying waste to creation, using it as a perpetual playground for his debauchery. Trouble is, he spend as much time quelling rebellions and bringing to heel ‘lesser’ demons lord who are barely weaker than he is.
Stats: Unlike Asmodeus, he should be killable. Solo level 30 to 32.
Hedonistic sadism: Moloch wants to have fun. Power is only a mean to an end, not an end. It brings him the freedom to do what he wants to do. And what he wants to do is inflict suffering. He likes battle, but he likes the aftermath even more because it comes with prisoners. He especially enjoy powerful and pure victim. In absence of such quality prey, millions of mortals screaming in agony are a fine substitute. DMs do have a responsibility not to alienate players but having Moloch’s fiends as enemies should also be an opportunity to push the envelope. It’s kind of a DM version of the Aristocrat joke. There is no avoiding this; this is a foe that revels in massacre, in rapes, in torture, in torment.
Divide to conquer: To maintain power, Moloch has to create conflicts between the others powerful demons, both his underlings and those he doesn’t command. That doesn’t make him nearly as Machiavellian as Asmodeus; demons aren’t that hard to goad. But the point is, unlike devils, the Demons are self-destructive. The same is true of their mortal followers. An adventure involving Moloch’s forces should involve inter-villains squabble if possible. If there are more than one figure of authority (whether actual demons or lesser followers), there should be tension. The lower ranking villain wants to become top dog and the higher ranking villain knows it.
Rivals to supremacy: There are other demons lords. Feel free to introduce another powerful demon at odds with Moloch. Just remember that Moloch is more powerful and is actively trying to bring him down. Like, right now. It should inform every action that lesser demon lord is taking (meaning he is in survival mode).
Berseker: Moloch himself is more about the sadism, but many of his fiends are all about the savagery of combat. They should behave accordingly.
Ultimate Goal: Fun. Acquiring a large and heavily populated tract of land along with a few powerful beings would make him happy for a few generations. Most of the faithful demon lords want to provide this for Moloch in order to gain his favours.
Flaws: Did I mention berseker? Most demons shouldn’t be too tactical. Those who are shouldn’t be too brave.
In a nutshell: The barbarian hordes meet the hellfire club.
Forces: Demons. Lots of Demons. Debased creature of elemental origins (Titans, Djinns, archons...) Savage humanoids (Gnolls, Minotaurs and Orcs in particular), sadistic cultist, serial killers and rapists worshipping him etc.