Changelings don't need to sleep. Instead, they meditate deeply, remaining semiconscious, for 4 hours a day. (The Common word for such meditation is “trance.”) After resting in this way, you gain the same benefit that a human does from 8 hours of sleep. Languages.
By RAW changelings revert when they DIE but not when they are unconscious (it would be hard to maintain a long term masquerade if you revert when you sleep!). I bet suggested that a piece of a Changeling — such as cut hair — WILL revert, but that this is slow and may take up to 24 hours.
Most changelings don't know they're changelings.
Though they may always feel somewhat different or removed from human life, most changelings are too young to understand who they truly are.
Changelings reach maturity at about fifteen years of age, and they live about as long as humans do.
You can change directly from one form to another
This means there is no duration, and unless you revert or die you will remain in the new form.
Changelings cannot alter themselves enough to change physical sizes (i.e, changing from Medium to Small, etc). It is worth noting that while a changeling could technically shift into something like an aarakocra, their wings would be non-functional.
The short version is that a Changeling can shapeshift to a form that can produce sperm to impregnate someone, and can shapeshift to a form with a uterus and eggs to get pregnant, but a pregnant Changeling cannot shapechange to a form without a uterus without ending the pregnancy.
A changeling can eliminate or add traditional physical disfigurements - such as scars or birthmarks - when changing shape.
A changeling can make it LOOK like they have sharper teeth or claws, but this doesn't actually give them natural weapons; it's a deception. Essentially, it is a form of disguise self, NOT alter self.
Unlike doppelgangers, which are entirely genderless, a changeling does have a default gender that manifests in adolescence, but each changeling can adapt his or her form to be of either gender, hermaphroditic (both genders simultaneously), or entirely genderless.
Appearance. In their true form, or their form "at rest", changelings have pale skin, colorless eyes that can be completely white or completely black, and white or silver-white hair.
Most often it was thought that fairies exchanged the children. In rare cases, the very elderly of the fairy people would be exchanged in the place of a human baby, so that the old fairy could live in comfort, being coddled by its human parents.
Most often, the mother begins to carry twins, and one of the twins is a changeling. There are extremely rare cases of being born alone, or as part of triplets. In the rarest of cases, the other twin is a hag.
Changelings born from two changeling parents are born in their natural form: pale, slender, with colorless eyes and white hair.
They have large colorless eyes circled by thick black rings. Their hair color is most commonly a light shade of silver followed by platinum and blonde. In rarer cases, their hair can be pale shades of green, pink, and blue. Similar to elves, changelings lack body and facial hair.
Changelings don't inherently recognize each other. If they don't want to be recognized then when they do something suspicious it would be an insight check against the changelings deception, which the changeling has advantage on. A changeling could have expertise in insight from divergent persona.
Changelings do grow physically, to a point; as Changelings don't eat or drink, it is unclear exactly where the 'new' mass and energy come from.
Changeling blood is green, unlike most other animals. Changelings, despite their thinly and seemingly fragile frame, are capable of surviving otherwise fatal injuries thanks to their magical abilities.
Changelings typically have large eyes with narrow pupils, ranging in color from white, to yellow, to black. Hair colors are similar: Light grey, platinum blonde, shades of silver, all the way to the darkest hair color being a light brown.
17. As a playable race, changelings have the following abilities: Shapechanger: Using an action they can change their appearance and voice at will, even adapting their size between small and medium in some cases.
If you want it to be able to grow a tail when it changes into a tiefling or tabaxi, it is your choice. It is also your choice if you want the tail to be prehensile and able to grab and hold stuff. You can appear as a member of another humanoid race which will include things like tails, frills, gills, wings, horns, etc.
Powers & Abilities
In their human forms, the Changelings also appear to be immune to the effect of sunlight just like Stalklings, regardless if they are in their troll forms as well, thus making them the perfect spies for the Gumm-Gumms.
Changelings have red blood like a majority of the other races. Bleeding around others may alert many that the Changeling is not of the same race (should the blood color vary). For this reason, a Changeling will usually choose to take the form of a race with red blood.
Changelings have an interesting relationship with gender as a concept, which is probably part of the reason a lot of the art doesn't find it necessary to distinguish the males with facial hair. As they're changelings though, they can have any kind of hair they want.