For tabletop one shots, but especially for con games, and especially especially for highly
collaborative and/or GMless games:
How do you set desired tone and content we want/don't want to see?
How do you keep that tone/content and correct back if it strays?
1) Let's focus more on tone/content "I want the game to be full of idealism. I don't want the game to have sappy romances." and less on standard X-card "I don't want (horrifying thing/social taboo X)."
2) Let's also say that the option of "use the X-card for tone-checking" has already been considered. It's a reasonable option. But I want to hear other ideas.