Uxie is a wild Psychic-type Pokemon who appears a couple of times in the series In a Locked Room.
Uxie is the first of the three lake guardians to appear in the series. First appearing in Mass Attack, it took the role and disguised as the Heroic Heart, but it was regardless a combination of the characters' heroic hearts, and Uxie was just its core. Since it was the one to talk in telepathy, and also from those other heroic hearts, it guided every cloned character to the right paths and reminding on what to do. In the end of the room, it was revealed that it chose Rosalina because of her vast knowledge of the universe and tactics. The two of them communicated secretly, about how it and its other friends are the Mysterious Fusion Reaper's main targets, so that the world cannot be directly saved with the chosen ones. This means that the world is currently in danger.
Uxie will appear again but in an unknown room of Season 2.
Not much is known about Uxie, but it is implied that it is intelligent and knows where to guide on its allies. It is also implied that it is silent on other times.
None of Uxie's moves are shown so far. However, naturally, it can transform into a mirage.
- This Uxie is based on the Uxie from the Pokemon: Diamond and Pearl anime (Hence sharing the same English voice actress) and some of Fairy27's headcanon of the Uxie species in general.