The party I'm DMing is in the middle of Hall of Harsh Reflections and there is a warlock among them. Based on their recent run-in with a doppelganger, they have taken to asking the warlock to detect magic to ferret out any other shapechanger.
Now Detect Magic detects magical auras, and the doppelganger's change shape ability is supernatural which is defined as magical. So does this mean a cantrip type spell is sufficient to uncover the presence of doppelgangers by the third round of concentration?
On the other hand, supernatural abilities are not subject to spell resistance and dispel magic, so I am inclined to group detect magic among them.
However, I would really feel better about it if there was some reference I could cite. Any thoughts on the matter? I'd appreciate it if you could point out a ruling that I might have missed or if you have an opinion on how to best deal with the situation.
Thanks!