The Move Deleter is the guy you see whenever you have a movie that you want a Pokemon to forget. This guy is able to make a Pokemon completely forget about a move at no cost. Furthermore, you can now choose which Pokémon are in your group and which ones are sitting in your chest. Here you can find the Move Deleter in Pokemon Brilliant Diamond and Shining Pearl.
It will take some time to get to Move Deleter. Be prepared to play through a good part of the game first. During your journey, you will meet a non-playable character named Cynthia. After she helps you out in a few areas and helps her deliver ancient magic to her grandmother in Celeste Town, you will be tasked with defeating the leader of the Gymnasium in Hirthum City. Once this is completed, you will be assigned to go to Kanalaf City.
To reach the city of Kanalaf, you will need to move in stealth waves. Cynthia’s grandmother gives you this TM when you talk to her in Celeste Town. You may also like TM for Fly. This can be found at the Team Galatic HQ warehouse in Felston. You can walk or use the Fly back to Jubilife City. From there, head west to reach the town of Kanalaf.
After getting into town, head north and go to the building behind PokeMart. Inside you will find Move Deleter.
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