I've always been sorta annoyed at how the Fey in D&D. are essentially just monsters, without the proper otherworldly nature they should have. Therefore, I've been wanting to home-brew a trait to give certain fey that reflect their power over names. What. do you think?

Ownership of Names

If a creature tells the fey its name without taking proper precautions*, the fey can then take possession of that name. While the fey is in possession of the name, its original owner suffer disadvantage on saving throws against the fey's magic, and the fey can use its magic to impersonate the creature. The impersonation works similarly to a permanent (until dispelled) Disguise Self spell, and the fey has advantage on deception checks while posing as the creature.

*"Proper Precautions" means something like saying "I can tell you my name, but you cannot have it"

This is an ubsurdly powerful ability, I would say limit it to the most powerful Fey (Archfey and the like), you could have a camapgin based on this type of creature. Maybe have the Fey gain the name whilst disguised in the material plane. I would not make this a trait of all Fey as the Races Centaur and Satyr (from Mythic Odysseys of Theros) would get it by default as well, and giving players an ability THIS powerful is dangerous. Also the Conjure Woodland creatures would backfire immensely.

TLDR Super strong ability but limit it to only the strongest NPC fey otherwise the players can turn it against you.

As a player I would love this idea... it opens up all sorts of cool possibilities like the Fey trying to disguise themselves as non-Fey to try and get you to say your name without the precautions, and maybe even quests to "get your name back."

You should tell the players ahead of time, in Session 0, that this is a campaign setting rule, so they are on guard against it. You probably should make it known in the world not just to the players. I wouldn't have this happen to a PC without the character and player knowing it is part of the game.

I do think as a DM, Mathemurgy is right, you want to limit this so PCs cannot have it.

I'm probably going to have to steal this for a certain fey-heavy campaign I'm running... It's very good, but should definitely only be wielded by boss fey.

Happy to be of help

The practical effect of true names being magically potent is that everyone uses aliases, and asking someone for their true name is at a minimum like asking someone "What's your social security number" and possibly like asking them "What's your bank account password".

Yeah, this is consciously or unconsciously derivative of the power over fiends granted from knowing their true names.  World building wise, it's kind of neat.  At the same time, I don't know if I'd want my groups PCs necessarily subjected to something with this level of mechanical consequences over something that's role played away from them.  If Fey in the world are commonplace, you wind up with Pantagruel's scenario where there may be a whole magical industry of identity protection, maybe even powerful magics where you forget your true name.  If it's a rarity and something introduced with a potential player as victim, I feel there should be some sort of contest over saving the players name before it's outright possessed.  Maybe it's the name manifests itself in some sort of arcane tape or ribbon, like encode thoughts, and the PC can make a save to grasp it before it winds up in the Fey's hands, and then hijinks ensue.  

I was running a malformed wood elf character who was born in the feywild.

Forced into exile with her elderly grandfather as her tribe wanted to abandon her to die in the Feywild as she has the appearance of a particularly plain human child she has three names.

Vall her child name and the one she currently uses.

Caileyn Rothenel the name her Grandfather gave her and the one she used when she was briefly married.

And Edledhia meaning literally to go into exile is the name her tribe gave her as her mother declared Vall had been stillborn and angry at the actions of Vall's grandfather officially named her Edledhia something Caileyn didn't find out until she fled back into the Refuge (that was both her childhood home and prison within the Feywild) with her 6 year old son.

Only members of her tribe know her true name as she doesn't use that otherwise, it will be interesting if I ever get back to running this character and a foe tries to use either of the two names she has used in the outside world or the reactions of the other PC's if they encounter members of her tribe and they call her by the name they gave her!

I ran an encounter where the party stumbled upon a mysterious theater troupe in the woods where the lead role's ankle was injured and they needed a stand in! They called out to the rogue in the party (of noble background, meaning a powerful name) and asked her to stand in. Her pride wouldn't let her say no, and after a masterful performance the troupe leader said "That was fantastic! Could I please have your name??) she gave it, he smiled creepily, said, "Gotcha!" and the whole troupe vanished and the party fell unconcious.

When they woke up, no one was ABLE to say the rogues name because the fey LITERALLY took it! all that was left was a small bag of gold (cause they fey were being fair and "bought" the name instead of stealing)

They eventually used remove curse and got her name back. But they still had the gold so I made sure to keep in mind that the fey of that forest would be particularly hostile since the party "stole" back what they had fairly purchased

Quote from Mathematurgy >>

This is an absurdly powerful ability....

Disadvantage on saves vs magic from the name-holder and a free 1st level spell --- how does this amount to absurd power? 

Maybe b/c I assume that if this is the case, then everyone would be using name-security measures. Just give your PCs a chance to pick a 'true' name and off we go.

Am I missing something?

A better way to do something very similar is simply to use the spell Raulothim's Psychic Lance.

If you do not want to give them all that spell, you could make an ability similar to it.  For example, consider this feat I just made, takeable only if you are Fey:

Name Magic

If you speak a creature's name while casting a spell that has a saving throw and targets just one creature, you may choose either the regular save, or switch to an Intelligence based save.  In addition need not see the victim as long as they are in range.

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Another thing to consider is to NOT boost their power in any way shape or form.  Instead, simply make Fey alien by changing the way their role play.

To me the stories about Fey center more about strange behavior and desiring things that have no value to us.  They try to trade for things like sunshine, names, memories of your father, the scent of butterflies, the sound of a child's laugh.    

I would come up with a list of 20 such things and have them necessary to level up to 10th, 15th and 20th level.  Even the lower level creatures would seek to gain them in preparation.  In addition, they could 'trade' them to older more powerful creatures in exchange for favors.

So I have a question (I apologize if it has already been answered), but how would a PC go about getting their name back? Only through completion of a contract with said Fey? Through killing the Fey? Both sound very uncreative and was wondering if anyone had any other ideas.

Killing the Fey is the boring way. If you're clever, you can get the fey to return it willingly, or perhaps bargain for it.

Pull a reverse Uno by asking "Hey, could I have that name again?"

In 3.5e, true names weren't just a character's given name, but a name translated into a fundamental cosmic language. An individual would generally not know their own true name unless they were willing to do quite a bit of research. In that setting, I'd feel much more comfortable using variant rules around true names because they were much more difficult to learn, and even if learned, would require a practiced tongue to pronounce correctly. Moreover, an individual's true name could subtly change over time as the character grows and becomes more experienced.

In wild beyond the wtich light there were domain laws which were magical laws enforced by an arch fey. These were things like 

• Reciprocity, if offered a gift you had to return the favor 
• Hospitality, you had to be kind to guests
• Protection, you cannot harm certain things  for example children 

With those kinds of rules you can have the fey effects. 

 If you want a fey like effect I had a feat I created for a fey based character:

If they got a creature to accept a deal or gift they could cast an enchantment or illusion spell on them  or themselves   as a reaction and without somatic or verbal components.  In addition their proficiency bonus would then be subtracted from any saves or checks against the spell. The caveat is the spell had to be related to the deal or gift; or a fey law. 

This was designed for fey players be able to do things like say " accept this rose as a friend" and cast charm person as part of that if the creature accepted or in the name stealing example you might say " can I have your name" and cast disguise self to look like them with all creatures having your proficiency bonus subtracted from checks to discern it. 

Its also fairly flexible for example also with taking a name you could use a 9th level spell to cast modify memory  to erase their identity or if there was a fey law in that realm like  "obey your parents for they gave you your name" you could rewrite your self to be their parent and the fey law would kick in against them.

It would vary. They could trade for it. Use a wish spell. Or perform a task. Their name can also be represented as an object that was precious to them so they can steal it back. However do not kill the fae your name would likely be lost forever. 

That's so creative! Would you kind if I bring this to my dm?

Would it make sense for a Hag to have this ability?

Quote from TheAlmightyScriptKeeper >>

Would it make sense for a Hag to have this ability?

 Definitely, the importance of names is a bit of a mainstay of magic generally and hags as a kind of witch stand in go particularly well with them. 

I feel like it's less powerful than it seems, because while the effect is quite potent it can also be denied to the NPC by the player with like one sentence of roleplay.  It reminds me of Uno, where the official rules state that you must say Uno once you're down to one card and if you forget to do so and the next person takes their turn, anybody at the table can simply point it out and you need to draw two.

Giving the ability to force any player to draw two cards even when it's not your turn is extremely powerful, but the power can be denied just by being slightly vigilant.  Which, in the Feywild or when dealing with Fey is kind of the point - these folk are tricky and crafty and they do not mean you well, so watch your tongue and think before you speak because in this place oral contracts are considered valid.