Is there anything you consider "out of bounds" in terms of content for any AU? Like you won't put a character through ABC because XYZ?
I usually keep AU themes as close to the original contents themes as possible. It may have gotten a little out of hand with mermaid AUs, but I usually strive to keep everything as In Character and Rekevant as possible. I’ve reconstructed entire plots for AUs (the Frozen AU is a big one).
In terms of what I won’t put a character through: if it’s not relevant to the story, I don’t put it in. I don’t like senseless violence or angst just for the purpose of angst and making the characters miserable, because at that point tit doesn’t make sense and I’m not invested or feeling sympathy for the characters, I just feel Bad. There’s LOTS of things I could do to Jekyll in LOTS of my AUs but I hold back.
The Severed Head ending for the Frozen AU was PURELY for the drama of it and increasing the stress level but it’s not canon to my actual AU because at some point the angst just rises so high that it doesn’t feel satisfying anymore. I had a third even MORE upsetting ending that I discussed with my friend a while back but honestly it was just Too upsetting and had so many plot holes.
Angst/Hurt is good when it’s done in well thought out doses and done tastefully and true to the story. You gotta let it Sit, Simmer, stew, until it boils over~