So how often do other DMs roll ability scores for their villainous NPCs, most specifically non-humanoid ones. For example, say I want to create a unique black dragon encounter. He isn't THE BBEG, but is a legitimate boss fight. But he's not just some black dragon Mook. He has a name, quirks, all that. Do you roll ability scores, give him maybe a couple different spells or spell-like abilities? Or is he just another 'adult black dragon'?
Or does it have to do with player composition? I have a fairly in-depth story, where the NPCs all tie together at this stage. My players enjoy the depth of the world, but I know some wouldn't. Would you do the encounters differently, depending on play style?
I can only assume that you make your PC's roll for ability scores too. Either way: gross. I don't see any benefit to determining the scores of an NPC randomly, it just makes it more difficult to ensure the character can do what you want them to do (oops my LE prosecutor ended up with low mental scores and is now bad at his job and incapable of misleading people).
I normally don’t roll stats for any NPC’s. If I want to make a unique NPC I simply adjust what needs to be adjusted to make the creature I have in mind. As a GM I don’t have to follow any set of rules when creating a monster or encounter for the players. To me this is simply something any GM is able to do.
About the only NPC I would consider rolling stats for are unimportant NPC’s that don’t really have any part in the actual plot. Those type of NPC’s rarely have full stat blocks anyways. In that case I will either assume a 10 or possibly roll for just that stat. So if one of the players decided to cast charm person on the blacksmith I might roll to see what his WIS is for purpose of making the save.
If you want to customize the black dragon simply change what you want. Swap out spells and feats as you see fit. Adjust any stats you want, but be careful not to go too far. I would keep the standard black dragon abilities as those are the equivalent of racial abilities.
Rule #1: Beg, borrow, and steal everything you possibly can to make your campaign easier to generate
If I was building a unique Black Dragon I would start with an existing black dragon and tinker with the ability scores present. For instance, with an Adult Black Dragon I'd start by rounding the stats up. Then I'd push the HP higher, probably 75% or maybe even 90% depending on the party. From there, you can tinker with feats or slas. If I was really feeling fancy, I'd add in some class levels. Swap his wisdom over the Charisma and give him three levels of Anti-paladin and a conductive amulet of mighty fists to let him channel touch of corruption through his melee attacks and force saves.
I don’t necessarily roll stats, but I do roll hit points using the same method I make the players roll for major NPCs.
I think the standard arrays are fine. If you think a particular villain needs better stats, then just give them the advanced template.