The definition of a Changeling's shapeshifting ability in Mordenkainens (not Eberron) says ...

As an action, you can change your appearance and your voice. You determine the specifics of the changes, including your coloration, hair length, and sex. You can also adjust your height and weight and can change your size between Medium and Small. You can make yourself appear as a member of another race, though none of your game statistics change. You can’t duplicate the appearance of an individual you’ve never seen, and you must adopt a form that has the same basic arrangement of limbs that you have. Your clothing and equipment aren’t changed by this trait.

I have a player that is asking me what DEMONS he's seen in our campaign ... probably because he assumes that his changeling character can change into them. While his new form wont have a demon's powers, that still seems a bit overpowered to me. While the DM does have final say, I would like to refer to the official rules to NIX this idea if I can. So, some questions...

1. Are demons considered a "race"? If not, he can't turn into them. 

2. Can changelings only change into humanoids? It doesnt say so directly, but it does say they "must adopt a form that has the same basic arrangement of limbs"?

Any other thoughts or ideas about rules that may help in my discussion?

Quote from Jabbamonkey >>

The definition of a Changeling's shapeshifting ability in Mordenkainens (not Eberron) says ...

As an action, you can change your appearance and your voice. You determine the specifics of the changes, including your coloration, hair length, and sex. You can also adjust your height and weight and can change your size between Medium and Small. You can make yourself appear as a member of another race, though none of your game statistics change. You can’t duplicate the appearance of an individual you’ve never seen, and you must adopt a form that has the same basic arrangement of limbs that you have. Your clothing and equipment aren’t changed by this trait.

I have a player that is asking me what DEMONS he's seen in our campaign ... probably because he assumes that his changeling character can change into them. While his new form wont have a demon's powers, that still seems a bit overpowered to me. While the DM does have final say, I would like to refer to the official rules to NIX this idea if I can. So, some questions...

1. Are demons considered a "race"? If not, he can't turn into them. 

2. Can changelings only change into humanoids? It doesnt say so directly, but it does say they "must adopt a form that has the same basic arrangement of limbs"?

Any other thoughts or ideas about rules that may help in my discussion?

 

1. Demons are not technically a "race", but I think it's very unlikely that the use of the word "race" there was intended to be a limitation on what kinds of creatures a Changeling can transform into.

2. No, Changelings are not limited to changing into humanoids. But keep in mind that "Humanoid" has a specific meaning in D&D that goes beyond its general meaning in English. Changelings themselves are not Humanoids. This is why it says "basic arrangement of limbs" instead — if they wanted to limit it to the D&D creature type "Humanoid", they would've said that.

The key thing, I think, is what you define as a "limb". A lot of demons in D&D have things like tails or wings. D&D does not have any official rules that I'm aware of on whether these count as "limbs". If those are limbs, then this character can't change into the form of anything that has them. If they're not, then they can.

Also keep in mind that the change is purely aesthetic and does not confer any of the abilities normally associated with the form. For instance, even if you did allow changing into a form with wings, the character would not gain the ability to fly.

"appear as a member of another race" is the sentence that is giving me difficulty. If it were just humans (not humanoids!), race would be any cultural group sharing physical traits (asian, indian, caucasion, etc.). BUT, D&D has many "races". I guess my question is, are demons a "race" or are they something different?  The PHB lists many "playable races" .... but are many monsters considered a race of their own?

As for limbs... take a bearded devil for example. It has 4 limbs .... but it has a writhing barbed beard. Can a changeling duplicate that visual effect?

A mezzoloth has 4 limbs, but has a chitinous insect-like body. While a changling "...determine[s] the specifics of the changes, including [their] coloration, hair length, and sex ..." does that include a chitinous shell-like covering?

Even if you restrict the Changeling to “races” in the player character sense, that implies they can form: 

- a shell (Tortle)

- scales (Dragonborn, Lizardfolk, Kobold)

- feathers (Kenku)

- hooves (Satyr)

- horns (Tiefling, Satyr, Minotaur)

- tails (as for horns, plus Tabaxi, Kobold)

- armoured or inorganic hides (Warforged, Autognome).

Only Centaurs, Fairies, Aaracockra,, Owlins and Thri-Kreen are excluded by having additional limbs. (Plasmoid is a tricky one: do their arms and legs count as “limbs” in an anatomical sense??) 

There’s nothing there that seems to exclude chitin or motile beards. 

(disclaimer: using 2014 text)

I'd say races are a subgroup of a particular creature type, based on some wording I've come across (nitpicking is my second name):

From the 2014 Ranger:

Favored Enemy

Beginning at 1st level, you have significant experience studying, tracking, hunting, and even talking to a certain type of enemy.

Choose a type of favored enemy: aberrations, beasts, celestials, constructs, dragons, elementals, fey, fiends, giants, monstrosities, oozes, plants, or undead. Alternatively, you can select two races of humanoid (such as gnolls and orcs) as favored enemies.

2014 MM:

Elementals are creatures native to the elemental planes. Some creatures of this type are little more than animate masses of their respective elements, including the creatures simply called elementals. Others have biological forms infused with elemental energy. The races of genies, including djinn and efreet, form the most important civilizations on the elemental planes. Other elemental creatures include azers, invisible stalkers, and water weirds.

Humanoids are the main peoples of the D&D world, both civilized and savage, including humans and a tremendous variety of other species. They have language and culture, few if any innate magical abilities (though most humanoids can learn spellcasting), and a bipedal form. The most common humanoid races are the ones most suitable as player characters: humans, dwarves, elves, and halflings. Almost as numerous but far more savage and brutal, and almost uniformly evil, are the races of goblinoids (goblins, hobgoblins, and bugbears), orcs, gnolls, lizardfolk, and kobolds.

Interesting (link to sageadvice.eu):

@Natronmeanz99 would love it if you could put this one to bed. Can Rangers choose ‘Goblinoid’ as one of their races in regards to Favored Enemy?
@JeremyECrawford If you're choosing a type of humanoid for Favored Enemy, goblinoid is too broad, but goblin, hobgoblin, bugbear, or the like works
@JeremyECrawford More about Favored Enemy. It tells you to pick a creature type, but if you pick humanoid, you choose two races of humanoid. Goblinoid isn't a race. As explained in the Monster Manual, goblinoid is a family of races. Goblin, bugbear, and hobgoblin are races
@Lich_Well Why doesn't the stat block for them have humanoid (goblin), humanoid (bugbear) and humanoid (hobgoblin), but instead they all share the same descriptor of humanoid (goblinoid)? If the intent was to treat them as separate races, the stat block communicates that very poorly.
@JeremyECrawford A monster sometimes has a tag in parentheses right under its name. A tag can communicate a variety of things. "Shapechanger," "titan," and "goblinoid" are examples of tags. For more information, see "Tags" in the "Monster Manual" (p. 7)

I told my player, that I'm ruling as the following (since DM has final say)...  Note: This is D&D 5e, and not 2024 rules (that don't even use the word "race" anymore)

As an action, you can change your appearance and your voice.

I'd say that you can't duplicate a specific person's voice, but the changeling can adequately sound like someone from that "race"

You determine the specifics of the changes, including your coloration, hair length, and sex.

Sounds fine, but I'd rule that looking like a "specific" individual would require some rolls (similar to a disguise check).

You can also adjust your height and weight and can change your size between Medium and Small.

This one I had some issues with. The word adjust is VERY vague. Does that mean that a 100lb. changeling could change into a 300lb person. My player tried to argue that it would be like wearing a "fat suit" ... and I argued back, "so he's filled with air inside?". He said that Changelings were "magical" creatures, and I argued back that it was a physical transformation (not an magical illusion), but even a magic ability had to have some limitations (and a "fat suit" really stretched the imagination).  In the end, I decided that I'd limit the size change to around 50lbs in either direction. So, he could become SMALL, but he'd be a tall SMALL. He could become BIG, but could only stretch his physical limits so far....

You can make yourself appear as a member of another race, though none of your game statistics change. You can’t duplicate the appearance of an individual you’ve never seen, and you must adopt a form that has the same basic arrangement of limbs that you have.

The word "race" is very open ended in DnD 5e. Are races just the "playable" races, or do they include Devils, Demons and other monsters? Is a mimic a race (I'd argue more of a species)?  

If we were just starting a new campaign, I'd limit the changeling's shapechanger ability to be JUST be playable races (that are still plenty of options). That would make life alot easier as the DM. BUT, because we were already several months into a grand campaign, I felt I couldn't make such a large change (I should have done it at the beginning, when he was decided on characters to play ... but I didn't know this would come up ... and he probably just thought "I can be ANYTHING"!). Instead, I had to place some restrictions based on the game's definition.

I decided to allow any "race" (any human shape) ... BUT, I used the "basic arrangement of limbs" to restrict the changeling's shapechanger ability. "Limbs" mean arms and legs, but I felt it also included any long appendages (like wings on your back, long tails, tortle shell) -- since these would all require a changeling GROWING those limbs/appendage.  However, I did allow some smaller things, like horns (i.e. minotaur, Tiefling) and short tails (harengon). It seemed more logical that he could add small features.

I felt like that was an even compromise. It was a similar argument about "adjusting" weight." You can change within reason ... but not EXCESSIVELY. 

While Fey, Changeling are bipedal with corresponding arrangement of limbs (head, arms, body, legs) and thus can change appearance of race, voice, coloration, hair length, sex, height, weight and size between Medium and Small without changing any other game statistics, clothing or equipment.

Changeling should thus be able to appear as some race of wingless devil or demons if wanted.

Quote from Plaguescarred >>

While Fey, Changeling are bipedal with corresponding arrangement of limbs (head, arms, body, legs) and thus can change appearance of race, voice, coloration, hair length, sex, height, weight and size between Medium and Small without changing any other game statistics, clothing or equipment.

Changeling should thus be able to appear as some race of wingless devil or demons if wanted.

Agreed. I think a good general rule of thumb is that the Changeling feature allows you to change your appearance, but not your abilities. You can use it to trick people into thinking you're someone you're not, but it won't let you physically do anything that you couldn't do before.

Quote from Jabbamonkey >>

The definition of a Changeling's shapeshifting ability in Mordenkainens (not Eberron) says ...

As an action, you can change your appearance and your voice. You determine the specifics of the changes, including your coloration, hair length, and sex. You can also adjust your height and weight and can change your size between Medium and Small. You can make yourself appear as a member of another race, though none of your game statistics change. You can’t duplicate the appearance of an individual you’ve never seen, and you must adopt a form that has the same basic arrangement of limbs that you have. Your clothing and equipment aren’t changed by this trait.

I have a player that is asking me what DEMONS he's seen in our campaign ... probably because he assumes that his changeling character can change into them. While his new form wont have a demon's powers, that still seems a bit overpowered to me. While the DM does have final say, I would like to refer to the official rules to NIX this idea if I can. So, some questions...

1. Are demons considered a "race"? If not, he can't turn into them. 

2. Can changelings only change into humanoids? It doesnt say so directly, but it does say they "must adopt a form that has the same basic arrangement of limbs"?

Any other thoughts or ideas about rules that may help in my discussion?

 

 Race used here is the game term Race, which is now Species in 2024 rules. They gain none of the mechanical benefits of any change however (such as horns or claws that can stab or slash). They are purely for show.