This is a video of a talk by a really good friend of mine, Mo Holkar.
He talks about the middle ground between characters entirely created by players and characters entirely created by the Larpwright. It is interesting in and of itself but I think there is some really good stuff in here for prepping one shot TTRPGs. Especially where you want to create or partially create characters ahead of time, or if you are presented with a partially created character at a convention game.