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Dr. Moss (Japanese: ドクター・マスダ Dr. Masuda) was a character of the day in Delcatty Got Your Tongue, seen only in flashbacks. He didn't have a speaking role.
Dr. Moss was Dr. Abby's teacher in the techniques of massage therapy for Pokémon, much like shiatsu. He gave her the Moon Stone that evolved Dr. Abby's Skitty into a Delcatty, teaching her that Abby had to 'evolve' herself much like Johnny had.