I could talk about Antagonists and Monsters today...

But, before that. #DOMAIINS doesn't use the word NPC as it makes no sense in the game's narrative and mechanical structure.

So any character that isn't the player's doesn't have stats, they aren't needed. If there's something to do with them, the players engage with their character's Animus Aptitude.

Due to that, there's no need for stats as these are already accounted for in the Character.

Now what if something needs to happen with an "npc" to further the game?

Still nothing. Just continue like they are backdrops but assign a difficulty from the Set-Piece to the character.