Azelf is a wild psychic-type Pokémon who appeared a couple times in the anime.
Azelf is the second lake guardian to appear in the anime. It chose to connect with Ash because he used his strong will power to protect Pokémon. Ash first encountered Azelf at Lake Valor in Pruning a Passel of Pals! after he was having a hard time sleeping because he was worried about how he would do in the Wallace Cup. In the middle of the night, he walked and looked out on Lake Valor where he saw Azelf's projected soul. It wouldn't be until The Needs of the Three! that Ash would see Azelf in its true form. Azelf contacted Ash in his dreams warning him of the destruction of the world. Azelf was awakened from its sleep after Pokémon Hunter J dropped the Galactic Bomb into Lake Valor. Ash actually felt the shock wave of the blast because of his connection to Azelf. Azelf tried to fight off J, but it was eventually captured. Mesprit and Uxie attempted to rescue it but they were captured as well. While at Galactic Headquarters, Azelf called on Ash and teleported him to the base. Cyrus was able to take control of Azelf'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. Ash was able to successfully set Azelf free by telling Pikachu to use Thunderbolt to break the Red Chain piece that was controlling it. With their hearts bonded, Azelf and Ash were able to help calm down Dialga and Palkia and save the world from destruction. Afterwards, Azelf said goodbye to Ash and went back to sleep in Lake Valor.