Dear Secret Mutant,
Thanks so much for coming here to check this out! I don't have a list of bookmarks/favourites and I haven't written very much in the fandom, so I've written quite a long letter to make up for that.
First of all, feel free to ignore all four prompts completely and write something completely different! As long as you've made something you've enjoyed making, and it avoids my do-not-wants, I'm sure I'll love it. But if you do want some further guidance, here goes:
I originally got into this fandom for the former-lovers-to-enemies Xavier/Magneto storyline, so feel free to pile on the angst, regrets, painful memories, UST etc. (But don't panic if that's not your thing. I do read happy fic too!)
I tend to prefer fic that's either completely faithful to canon (movies or comics) insofar as that's even possible with so many internal contradictions ;) or else is canon-divergent in the 'what if?' sense, like what if it were Charles who was locked up for supposedly shooting Kennedy (not a prompt, just a random example!). I definitely don't like non-powered AUs. If you want to write an AU, go for it :) but I'd prefer if they were still mutants, and at least some of the main themes of the movies (mutant politics, divergent ideology etc.) were still there, at least a tiny bit.
I'm fine with unhappy or bittersweet endings, also with happy fix-it endings. Also fine with any rating from G to NC-17. Unless you're writing gen, I'd prefer the main pairing be Erik/Charles, but am fine with any background pairings you like. I like the Patrick Stewart and Ian McKellan era as much as the XMFC era, so feel free to focus on either one.
canonfic, or canon-based AUs
outsider POV (i.e. Erik/Charles from the POV of a third character)
Erik speaking German, French or whatever else (but please get a beta-reader if necessary and don't just use Google Translate ;D )
mutations as a metaphor for other forms of prejudice, political and sociological discussion, historical details from the 40s-80s
Charles still being in a wheelchair, in AUs and in canon if that fits with the timeline (in particular, if you're writing post-XMFC fix-it fic, I'd prefer that wasn't one of the things you 'fix')
fic that doesn't gloss over the horrible things Magneto's done (not necessary if it's set before he's done anything much, of course!)
fic exploring how Erik/Magneto justifies his actions to himself, or how Charles deals with being in love with someone who has done what Erik has done
Things I'm ok with (these are not requests, they're just things that people tend to leave out of gift fic just in case, but that I'm fine with if by some chance you happen to want to write them): permanent character death, unhappy endings, gore, heavy angst, references to religion, kidfic (not mpreg!)
Please don't include: noncon, dubcon, incest, infidelity, mpreg, omegaverse, soulmates/soulbonding, suicide, only gay for you, RPF, underage (e.g. highschool AUs), genderswap, non-powered AUs
Finally, here are a few themes I tend not to read (but if that's what you always write then feel free to ignore this and go for it! If you enjoy writing it I'm sure I'll enjoy reading it): hurt/comfort, fluff, schmoop, curtainfic or domestic stuff, crossovers, misunderstanding trope
Art: Gen/friendship only please, nothing NSFW. Maybe everyone training or hanging out together, or in battle. How about Erik and Charles playing chess somewhere odd or unusual. Or Hank doing some kind of cool or crazy experiment? Or something where the focus is on the setting and not the characters. Art featuring Cerebro, for instance. Or anything else you like! If you'd like a bit more guidance, I tend to prefer art featuring action and dramatic stuff happening over art featuring domestic scenes and fluffiness. If by any chance you're a comics fan, then some comicsverse-inspired art would be cool too (in which case SFW Erik/Charles would be great too, if you like, in addition to everything I suggested above.)
Well, that's it. I love exchanges - I hope you have fun too!