Fae Death occurs whenever a changeling is killed by Cold Iron. The death blow must come from a cold iron weapon. If this tragedy occurs, not only does the changeling die a physical death, but their faerie soul can never be reborn in a mortal host. They are lost to the Dreaming for all time.
Per the race description, you revert when you die. Unconscious is not called out, so no reverting when unconscious.
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!).
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.
Lifespan. Changelings reach maturity slightly faster than humans and live as long as humans do, typically about 100 years.
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 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.
Obviously, a changeling's appearance can change at any moment, but they do have a true form. Their true skin is usually grey or pale white, and their facial features are blank slates to an unnerving degree. They're typically thin and gaunt, and their hair is usually silvery with an occasional green or pink tint.
Changelings born from two changeling parents are born in their natural form: pale, slender, with colorless eyes and white hair.
As for being tattooed, changelings can definitely be tattooed, and they can just as easily erase the tattoo with a moment's thought.
The true form of a changeling is a bit paler than a typical human with slightly elongated limbs. Their eyes are colorless and ringed by black as pictured in the artwork above by Julia Zhuravleva. They have no body hair, but the hair on their head can be platinum, white, or silver.
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.
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.
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.
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.
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.
Sometimes changelings are old, nasty fairies who revel in the sorrow they cause; or fairies with prodigious appetites for human food or mortal breast milk. Sometimes the changelings are fairies so old and worn out that their kinfolk have left them behind, happy to be rid of them in exchange for a plump human child.
Shapeshifting – Changelings can appear human, and are capable of shifting between forms in order to feed. Sharp teeth – Changelings have a lamprey-like mouth covered in sharp teeth that allow them to feed on humans. Super strength – Changelings have superior strength compared to humans.
If you're Irish, you know your child is a changeling if it's sickly and doesn't grow in size like a normal child. Another fairly obvious sign is if it grows a beard or has long teeth. Finally, your child might be far more intelligent than other kids that age, and possess unusual insight.
changeling, in European folklore, a deformed or imbecilic offspring of fairies or elves substituted by them surreptitiously for a human infant. According to legend, the abducted human children are given to the devil or used to strengthen fairy stock.
In some cases, the changeling grows up often being very loyal and caring to friends and family despite what they are. They often care more for their friends and family than they do themselves. Most changelings enjoy helping as they get older, but they often feel different, out of place.
They also take humans who offend them and transform them into strange creatures or keep them as servants. In some versions of the story of Tam Lin the bard, he went willingly. In others he was kept against his will. These are just a few examples of what they may do.