Permit narrators to more fully create characters
Instead of having players always pick from a list of archetypes, it might be useful (especially for those telling stories in pre-created universes) to have the option for the narrator to list characters that must be chosen from (and only one player per character.) This may already exist and I just don't know how to do it.

Narrators can now provide pre-made characters for users to choose from when joining a game. Thanks!
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Christopher Hall commented
This is a great idea, especially for narrators who might lose a player. They could then have another person "step into" that character and take them over without needing to necessarily re-write the story to explain it.
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Robert Guthrie commented
Also, it'd be grand to be able to then pull these NPCs into scenes to interact as something other than an obstacle. They could be there, complete with character portrait, for the narrator to use.