I tried to write thus post several times, but got repeatedly constructively side-tracked.
The bearded devil. It’s a goofy name, a goofy visual, and since it lacks flying or a ranged attack, it can’t even fulfill its prime directive.
It has two unique abilities which work nicely together: a poisonous bite* which prevents healing and a bleeding attack which can be stanched by healing. The bleeding attack sounds equipment based (so not good enough for just this monster), though, and the AC is way lower than I want from a frontend devil.
* I wish it were a bite! Beard lash. Whatever.
What I really want is a sort of legionnaire devil. I think that was a thing in 4e, but it was a sort of level-20 minion. I want a Challenge 3 monster, for hot swapping with the devil I don’t like.
Since I want undead in the legioms of hell, I could just use a wight. But instead, have some new monster.
Blood Devil. As Bearded Devil except:
AC 16 (scale mail)
Add Trait: Hell Stench: Any nondevil who must breath who starts adjacent to, or enters adjacent to, this creature smells its carrion stench. For 1 minute they are poisoned. While they are poisoned in this way they cannot regain hit points. Constitution save DC 12 negates, repeated at the end of each round.
Remove Attack: Multiattack, Beard
Edit Attack: Glaive: remove the save to avoid the bleeding effect.
Add Attack: Heavy Crossbow: As glaive, but range 80.
Blood devils are the shock troops of hell yadda yadda. They’re clad in lacquered red scale mail, wear horned helms. Each of the scales in their mail is a sharpened pen nib, beaded with blood; they smell of rust and sulfur. Their flesh is mottled grey-green.