It may be worth having a prompt card with some good trait questions to ask yourself when you bring the NPC into play.

For example:

- What function does this person serve in the community? - Who does this person actively like or dislike? Why? - Is there anything about this person that other people remark on ("he/she's big/ugly/too clever for their own damn good" etc) - What do they want from the Dogs?

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Also, it's a cool idea to observe Jared's Rule of Three for assigning Traits beyond the strictly 'functional'.