As for being tattooed, changelings can definitely be tattooed, and they can just as easily erase the tattoo with a moment's thought.
While changelings can shift forms into a humanoid of similar size, there are restrictions so as not to allow a changeling to "break" every social encounter they come across. Changelings cannot alter themselves enough to change physical sizes (i.e, changing from Medium to Small, etc).
You can appear as a member of another humanoid race which will include things like tails, frills, gills, wings, horns, etc. However, your stats do not change so you cannot use the tail prehensively, cannot breathe underwater with the gills and cannot fly with the wings.
While changelings can look like anyone, they do have a true form. Their natural look can be scary to some due to their lack of detail and distinctive features. Their skin tone is always pale, either white or light gray, and they tend to have slender bodies with limbs slightly longer in proportion to other humanoids.
Changelings have the unique ability to transform their body to look however they want, provided they keep the same arrangement of limbs they already possess. It is very rare to actually see a changeling in it's 'true' appearance. Even when disguised, changelings can instinctively recognize each other.
Within this description there are variants of changelings that show subtle differences. Some have opalescence in their skin (as if it contains various colors instead of just being white) and their eyes can be completely black.
Changelings born from two changeling parents are born in their natural form: pale, slender, with colorless eyes and white hair.
A changeling can't make the wings at all. If they had wings, like from a class feature or something, then they could look like an Aaracokra with wings because they will have those limbs at that point.
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.
A common way that a changeling could identify itself is through displaying unusual behaviour when it thinks it is alone, such as jumping about, dancing or playing an instrument – though this last example is found only within Irish and Scottish legend.
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.
Changeling Traits
Age: Changelings reach adulthood at the age of 16. Their fey heritage allows them to live much longer than humans, up to 200 years.
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, but not so much that your size changes.
Languages: You can speak, read, and write Common and two other languages of your choice.
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.
If a family member showed Changeling traits—a strange appetite or delight for destruction—the suspicious parent would crick them into grabbing some iron scissors. Iron would burn a Changeling, revealing their identity at once. Scissors could also be placed over the door to a house.
Changelings were fairies who had been left in place of a human child or baby who had been stolen by the fairies. The child was taken for one of three reasons; to act as a servant, for the fairies to receive the love of a human child, or for malice/revenge.
A mate to a changeling can be of any race; there are several examples of changelings being mated to humans, other changeling breeds and even Psy.
According to legend, the abducted human children are given to the devil or used to strengthen fairy stock. The return of the original child may be effected by making the changeling laugh or by torturing it; this latter belief was responsible for numerous cases of actual child abuse.
If the changeling has lost a limb, the limb is missing in every form they take. If they haven't lost a limb, every form they take has all the limbs the changeling normally has.
The Changeling's Shapechanger trait states: 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, but not so much that your size changes.
It's not widely known, but one of the few ways one may determine that a person is, in fact, a changeling has to do with their hands. Changelings generally do not have the skill to replicate "life lines," and sometimes even fingerprints.
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.
They're immune to sleep and charm effects, as well as (probably) a few more mental effects. They can change their size and mass, far exceeding the limits of the changeling. They can literally speed up their bodies, creating a haste effect practically at will. There.