Hey there, everyone. I think the way curses are handled in standard 5e is pretty boring. Curses in 5e are sort of just status effects from casting magic spells, and they can be easily lifted with Remove Curse or Greater Restoration, but I think that takes away from the mystery and power of curses as I understand them in fables. So for my setting I've added an additional class of spell called "true curses," or "karmic magic." The idea is that these kind of curses can only be cast when someone breaks a taboo that they had purported to accept. The more important and widely accepted the taboo, the more powerful the spell can be. Additionally, the curse can only be broken by triggering certain conditions, and the easier those conditions are, the more powerful the curse. A curse can also be reflected back with more power if someone tries to curse someone for something they didn't do, and a few other scenarios. This "karmic magic" is mostly just for antagonists, but I guess if the players want to use it, I'd let them.

So that brings me to my question... what kind of taboos would fey have? Elves? Especially interested in what they'd have in common. I understand the fey have a somewhat non-intuitive and greatly varied set of moral right-and-wrongs, and elves while similar in some ways are not the same.

Good suggestion, I will. :)

May I sugest https://filibusterfrog.tumblr.com/post/175731828433/elf-hair ?

Good artist, but I'm not sure that quite covers it. A taboo is something that is unheard of in a society. So for instance, in Game of Thrones, it's taboo to betray someone after inviting them into your home. Someone who breaks that taboo might be subject to a fated punishment of some kind. It's the same sort of thing here. I'm trying to figure out what an elf would never do, and what a fey would never do. The only thing I have so far is "break a promise/contract," but I think some fey don't even follow that, and elves probably don't either.

I believe the Fey will be a challenge as they are so widely grey in terms of moral and ethical beliefs.  It might be easier to approach them by type as each kind of has their own nuance that could make fine-tuning a set of taboos specific to them easier.  As an overall taboo I would think violation/desecration of the natural world (plants and animals) would be viewed by both Fey and Elves as a taboo and lead to repurcussions.

You're probably right; that's a good way to go about it. Obviously some evil fey enjoy rot and decay and suchlike, but I don't think they would have joined in on this curse anyway. ...And maybe if the land was desecrated in a way that didn't allow for rot, maybe that would be taboo to even those evil fey...

Maybe physical domination is also another taboo, although more minor?

Sounds logical to me.  Evil Fey would have a natural aversion to druid's and rangers and those trying to protect the natural order.

just some additional thoughts...

Fey blood seems inherently linked to charm or resistance to charm.  that could be another avenue to explore.  Those resistant to their charms could be considered offenders though i'd put this in the more minor category since it's most just impeding their attempt at having some fun.  And most especially anyone that is able to charm them would likely be seen as in need of some curse-based education.  I guess this could be more directly in opposition to their natural feelings of freedom and being uninhibited and uncontrolled.

The fey are also often described as having a trickster type personality. Anyone who got the better of a fey creature that survived may find that they have unfortunate luck for awhile or that belongings go missing. Not exactly taboo, but definitely a way to make things interesting. In mythology, the fey are also famous for making deals with people who are in a horribly weak position to bargain and then really punishing them if they try to back out of the deal.

In The Darkest Part of the Forest, there are these:

1) Always be polite.
2) Always do what they ask, unless it contradicts another rule.
3) Never thank them.
4) Never eat their food. (less a taboo than it is a precaution for mortals)
5) Never sing if you suck at singing.
6) Never dance. (another precaution)
7) Never brag--ever, at all, under any circumstances.

1, 2, 5, 6, and 7 are to prevent offense. 4 and 6 are to prevent being caught in their magic. The thanking thing prevents incurring debt to them which they are completely terrible about. You can say things like , “How generous of you,” but if you were to thank them, they assume you owe them a debt and they will collect. In fact, if you accept anything at all, it is best to clarify the acceptance of it as a gift freely given with no debt incurred by taking the gift. This should be done politely, but very clearly. If one can navigate this type of interaction without offense, the fey will generally respect them afterward if they are not of the more evil varieties.

Cool source that I wouldn't have ever thought to read. Thank you for that, and your input!

Indeed, those mostly sound like precautions. But I think they'll be very useful to me, all the same. It's going to be challenging to be as clever as spritely (heh heh) as a fey in conversation with my players, but if I can pull it off, I'm going to want each fey to pose some kind of hidden danger if the conversation/interaction isn't navigated well. Providing an NPC that can give them fair warning ahead of time would make any trap they are caught in feel fair. They should arrive in 2 sessions; hopefully I can pull it off. On the bright side, I don't think I really need to have any kind of literal map of  their travels in the Feywild.

Perhaps the politeness thing could be a taboo, though. I think even hags are (sarcastically) polite. Maybe not some other fey creatures like darklings or redcaps, though. And that's to say nothing of eladrin haughtiness, which could be taken as impolite (yeah, I know there's a difference between eladrin and fey). I'll have to think on it.