Unique Monsters are a term used to define enemies in Xenoblade Chronicles and Xenoblade Chronicles 2 that have higher stats and potentially unique skills and give more experience and Art Points than normal enemies when defeated. Unique Monsters have unique names and there is only one of each of these monsters in the world. Their Xenoblade Chronicles X counterpart are known as the Tyrants.
There is a total of 157 Unique Monsters in Xenoblade Chronicles. Unique Monster also have a specific track, "You Will Know Our Names", that will play whenever a battle is started with one of them.
List of Unique Monsters
Xenoblade Chronicles 2
In Xenoblade Chronicles 2 the Unique monster that are defeated by the party will not automatically respawn but a named tombstone will be erected where the Unique Monster used to spawn. When interacting with the tombstone the player will be given the choice to resurrect and rebattle the Unique Monster if they so choose.