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.
WotC has confirmed that changelings are considered to have the Shapechanger subtype. So they are indeed immune to polymorph and can be affected by moonbeam.
Charm is a mind affecting enchantment. Elves are immune, Fey are immune, Undead, oozes, plants, outsiders are all immune.
It might be related to most charm spells affecting specifically Humanoids, which makes the Fey immune to them, rather than just resistant. You could argue that magic like "Dominate Monster" was specifically crafted for them, which is why they're not resistant to it.
There are some Undead that I believe are listed as being immune to charm, but it's not standard across all Undead.
Immunity to Charm
Elves cannot be charmed, either by the charm person Magic User spell, the song of Harpies, the gaze of Vampires, the allure of Dryads or other effects. They are similarly immune to the love-charm of Nymphs, the blinding beauty of Sidhe and the fatal shriek of Banshees.
We can use the filtering options in D&D Beyond's monster listing to see how many monsters/NPCs across all sources are immune to each condition: Blinded: 97. Charmed: 290. Deafened: 79.
Never give them your name (Full or otherwise).
If a Fey asks for a humanoid's name and they say it, they're giving them power (and possibly partial control) over them.
Beginning at 6th level, you can't be charmed or frightened while raging. If you are charmed or frightened when you enter your rage, the effect is suspended for the duration of the rage.
The strength of the effects is related to the strength of Bell's feelings. As a side effect, it makes him immune to charms.
They can't be charmed, they can Read Thoughts, and they have the Ambusher and Surprise Attack features in addition to their Shapechanger power. All these abilities synergize to make the doppelgänger a sucker-puncher par excellence.
The Confundus Charm (Confundo) is a charm which causes confusion in a person or bewitched object. It appears that there are varying degrees of confusion caused by the spell, from simply tricking a person or thing about a specific incident to confusing a person to the point at which they endanger themselves.
There's no rule that causes monstrosities and aberrations to be immune to the charmed condition.
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.
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 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.
Just because you've charmed them doesn't mean you can compel them to action. Charmed creatures know that you charmed them after the charm ends. In many cases, this will cause the target to like you much less once the spell's effect ends.
A charmed creature still determine if its willing or not to do anything. Being friendly doesn't automatically make people willing, but it may facilitate it.
The mechanical defined effects of charmed are that the NPC won't attack you, and you have advantage on social interactions.
Names hold power. If a faerie asks for your name and you say it, you're giving them power (and possibly complete control) over you. The best thing to do in this situation is to give the faerie a made-up name or your nickname. However, if you know their name and say it, then they will leave you alone.
When looking at your little one's small precious features, you could almost compare them to a mystical fairy that charms you with their kind demeanor. If this is the case, the beautiful French girl's name Fae would be a lovely choice for baby.
Archfae, Fae, and Pixies are those fairies, they want to take True Names, and stealing away their owners is among the nicest things that can happen. When someone's True Name is taken, that person becomes a creature known as a Changeling.
The Monk isn't simply immune to being charmed, they must actively use an action to end the charmed condition.
Sure - if the creature isn't immune to being charmed, then you can attempt to charm them. Beware vampires, though — their legendary resistance allows them to succeed on any save they would fail 3x/day.
Yes. The spell says: "You attempt to charm a creature you can see within range." Any creature, no restrictions, even constructs, undead, fiends, elementals, etc.