What makes for a compelling one-shot to list here?

I'm a new DM running a homebrew 5e environment for my friends. Sometimes, I have a "creative" mechanic that I'd love to try out on a different group of guinea pigs first, before integrating it into  a longer campaign. Example 1: The party loses a battle, and evil surgeons trade body parts between the members. Example 2: The party is sent on a rescue campaign, only to find the party they are rescuing is their own doppelgangers. I give the players control of a second character for an extended period. What makes for a compelling one-shot, that folks here might want to try out? Text vs voice? Character level specified? Length of time? Weekend vs evening? Snacks provided ... oh, wait ... no snacks provided.

I think one thing that helps is to explain why this is a one shot.  From what I have seen, most one shots are last minute affairs created to fill a sudden gaming void.

Ahoy, Eric. Your question goes a little far afield for our forums.  We've touched on " What Makes a Great LFG Thread? " (stickied in this sub-forum), which you may find of use.  Further discussion on this topic would be better in that thread or on /r/rpg or /r/Roll20 .