It's Only Magic
Fey creatures sometimes kidnap a human child and leave a changeling in its place, tricking the human parents into raising an inhuman creature as their own offspring. The changeling has a foot in two worlds, living as a spy or sleeper agent for the fey, but thoroughly enjoying their life among humans.
Motive: Serving the fey; finding their place in the world
Health: 9
Damage Inflicted: Minor wound (3 points)
Movement: Short
Modifications: Might defense as level 2; deception, disguise, and stealth as level 4
Combat: Changelings use human weapons.
A changeling can use an action to alter their appearance for a minute or so to match that of someone they've seen. This is a reasonable likeness, although they may not know their target's mannerisms, accent, and other nonphysical qualities.
Some changelings are vulnerable to iron, taking an extra 1 point of damage from any iron or steel weapon.
Interaction: Changelings aren't inherently untruthful or untrustworthy, but sometimes they can't help but embellish a fact or take advantage of a situation. They otherwise act like regular people, but spending enough time with them usually reveals an odd quirk or attitude.
Use: An acquaintance is having trouble at home (because their family realized they're a changeling). Someone suspects a family member is actually a changeling.
Loot: Changelings have the same kinds of personal items that humans do, but they often have a token or other treasured thing that doesn't quite belong (and might secretly be a cypher or artifact).
GM Intrusion: The changeling moves out of sight as they’re changing their appearance; now they might look like a friend or blend into a crowd as someone unrecognizable.