https://bulbapedia.bulbagarden.net/wiki/List_of_Pok%C3%A9mon_by_anime_debutA weirdly comprehensive list, a fair few Megas and legendaries and that have only appeared in specials and movies. Latias, for example, has never appeared in a standard episode of the anime. The same was true for Mew until the Kanto episodes last year.
Otherwise, Golisopod, Kartana, Pheromosa and Melmetal have yet to appear, while some like Klang and certain forms like Red Flower Florges and Autumn Deerling have yet to appear in a standard anime episode.
