>>56087455As long as the custom moves don't get overpowered and have ridiculous utility with zero cost then they're fine.
I don't know the best way to implement them, but I do know the worst way to do that: by making the Character Main-dono the only person in the world to experiment with making new moves. Egads, no one has ever thought to psychically control fire before. Somehow all the other Delphox, Darmanitan, Armarogue, and Ninetales trainers completely overlooked it! Nani, wielding the attack energy like a sword? B-bakana!