Meloetta is a recurring Pokemon character in the anime that first appeared in An Epic Defense Force!.
History
Meloetta was first pursued by Team Rocket in Virbank City. It was able to elude them but somehow made its way into the Pokestar Studios where Ash had encountered it. After he saved it from a collapse of some tools it stayed close behind him, following him to Virbank Gym.
It reappeared in Rocking the Virbank Gym! (Part 1) and Rocking the Virbank Gym! (Part 2) where it watched Ash's battle against Roxie and was pleased to see him win.
Meloetta appeared again in BW087 where it was attacked by Team Rocket who had Woobat and Yamask attack it with Air Slash and Shadow Ball, respectively. Meowth then tried to catch it in an electric net but it was able to make it's escape. However, it was injured in the process and wandered into the street in a daze, almost getting run over by Cynthia's vehicle. Ash was able to recognize Meloetta from before and Cynthia applied potion to its wounds. Then they attemptedto get its fever down with a bag of ice. While Iris and Cilan searched for an Oran Berry for it, Ash kept watch.
After a little bit Oshawott came out of his Poke Ball sensing Meloetta's presence and instantly fell in love with it. Meloetta recovered a bit after eating an Oran Berry Emolga brought. During this time both Emolga and Oshawott were arguing with each other and Meloetta began to sing in order to calm them down. Afterwards, it disappeared once more but it had followed Ash and the others to Cynthia's jet.
In BW088, it followed Ash and snuck into Jeremy's car to Cynthia's villa. When Ash sees a Rattata, Meloetta appears and sits on Ash's lap. Seeing Ash, Meloetta seems very excited, when Cynthia says that Meloetta must really like Ash. A while later, they arrive at Cynthia's villa, but when Jeremy opens the door, Meloetta suddenly disappears again. A while later, when Ash and co. let their Pokemon see their old friends Dawn and Piplup her pokemon, Meloetta secretly comes. The Pokemon can sense Meloetta, and Ash knows it's nearby and calls it out to meet Dawn. Meloetta appears and Dawn get acquainted. Upon seeing Meloetta, Dawn's Piplup instantly fall in love with it just as Ash's Oshawott before it. Oshawott attacked him with Aqua Jet, upset to see Piplup and Meloetta gettting along, sparking a rivalry. During the battle between Dawn's Piplup and Cilan's Pansage, Meloetta was excited about the battle and was happy for Piplup.