Maybe a stupid idea, but maybe it already exists
You start a game of DnD with a blank character sheet. Your DM has them all. You only discover stats and things as they become relevant.
Like, “I rolled 7 on my constitution check”
“You get a +2 bonus so that’s a 9.”
*Hurriedly marking it down*
“I would like to ask the innkeeper if there is anything weird going on in the area”
“Dragonborn are rare in these parts, so she is suspicious at your approach.”
“Wait I’m a DRAGONBORN?!?”
It would be absolute chaos but for a one-shot I feel it would be fun. Maybe all the characters have amnesia and they have to figure out what they can do from scratch.