Have you ever written a piece that became a form, or even a genre, you hadn’t planned on writing in? Or do you choose a form/genre in advance?
Yes. I entered the IWSG mystery anthology contest a few years back. My story didn't make it in. It has a mystery element, but it's not really as much of a mystery far as the genre goes. There is no detective. There is "magic." And there are missing children. (They aren't runaways and aren't hiding.) It's really more of an Urban Fantasy, even though I tried to make it be a mystery.
Anyway, that's why I put it on Smashwords with the option for people to pay whatever they'd like. (Including nothing.)
**Update - September 2020 - This post was scheduled. For whatever reason, it never actually posted. I didn't even notice until the September post rolled around. August really was THAT messed up. Sorry.