In one of the Unearthed Arcana, the changeling from Eberron was introduced as a playable character race. It has a "shapechange" ability, which allows for a superficial polymorph to change their appearance.
Is this change detectable with a Detect Magic spell? Or is there any other way to detect the changeling's use of this ability?
Best Answer
Detect Magic will not identify a polymorphed Changeling.
Only spells (or abilities that replicate specific spell effects or invoke a "spell attack"), magical items, and effects specifically clarified as being magical by descriptive text count as capital-M Magic, which would be detected by Detect Magic. Otherwise, even something which would seem supernatural to us is just part of the "background magic" of the world, which is a part of nature and always functions, and is not considered magical as far as game rules are concerned (as per Sage Advice).
The changeling's Shapechanger ability states:
Contrast with, for instance, the Change Shape ability of certain dragons, which always has wording like:
The dragon's ability is expressly magical. The Changeling's ability is not. Therefore, effects that detect magic are no use in identifying a polymorphed changeling, though they would help you spot a polymorphed dragon.
There are, however, other means to identify a polymorphed Changeling.
Any being with Truesight can:
The most obvious way to gain Truesight is the use of the 6th-level spell True Seeing.
The spell Moonbeam also has an extra effect when it targets shapechangers, as failing to save against the spell forces them to resume their original form - though this is a damaging spell, so probably not one to use unless you're already on very bad terms with your suspected polymorphee.