Uxie is a wild psychic-type Pokémon who appeared a couple times in the anime.
Uxie is the last of the lake guardians to appear in the anime. It chose to connect with Brock because of his vast knowledge of Pokémon. It is so far the only legendary Pokémon that Brock has befriended. Brock first encountered Uxie at Lake Acuity in Uncrushing Defeat!. Brock went in search for a berry near the lake that would help Ash's Monferno recover from its injuries that it received during its battle with Paul. When he looked out on the lake, he saw Uxie's projected soul. It wouldn't be until The Needs of the Three! that Brock would see Uxie in its true form. Uxie contacted Brock in his dreams warning him of the destruction of the world. Uxie was awakened from its sleep after Azelf was captured by Pokémon Hunter J. It and Mesprit teleported to Lake Valor in order to try to save Azelf, but the two of them were also captured by J. Before being turned to stone, Mesprit and Uxie used Future Sight. When J was about to leave, the attack came from the clouds and struck her ship, sending it crashing into Lake Valor. Uxie was able to contact Brock through his thoughts. He was also able to feel its pain. Uxie eventually teleported Brock to the headquarters of Team Galactic. Cyrus was able to take control of Uxie's mind with a piece of the Red Chain which he implanted in its forehead. He took it and the other lake guardians to the Spear Pillar where they were all used to awaken Dialga and Palkia. Brock was able to successfully set Uxie free by telling Croagunk to use Brick Break to shatter the Red Chain piece that was controlling it. With their hearts bonded, Uxie and Brock were able to help calm down Dialga and Palkia and save the world from destruction. Afterwards, Uxie said goodbye to Brock and went back to sleep in Lake Acuity.