Truesight
A creature with truesight can, out to a specific range, see in normal and magical darkness, see invisible creatures and objects, automatically detect visual illusions and succeed on saving throws against them, and perceives the original form of a shapechanger or a creature that is transformed by magic. Furthermore, the creature can see into the Ethereal Plane.
This work includes material taken from the System Reference Document 5.1 ("SRD 5.1") by Wizards of the Coast LLC and available at https://dnd.wizards.com/resources/systems-reference-document. The SRD 5.1 is licensed under the Creative Commons Attribution 4.0 International License available at https://creativecommons.org/licenses/by/4.0/legalcode.