Updated.
Before we move on, there's still one matter to touch: the summoning. I was considering allowing Chernobog to summon festergogs (CR 9) and stygilor/tumor fiends (CR 4), but I'm not sure how many would be fair.
I'm not sure about the balor, but the nightcrawler does have the right touch of "fetidness" for Chernobog.
By the way, the abilities line is still blank. Are we using Str 26, Dex 22, Con 30, Int 27, Wis 25, Cha 29?
I'd make the summoning automatic.
Comparing to other demon lords in the CC, we might want to increase the damage of the hellfire a bit or make it at will or something. Maybe some SLAs would be good, too.