When you enter a contest, you will be up against three NPCs. Each of these characters has got a specific Pokémon that they will use in Contests and, as such, have a moveset that is catered to them. Each Pokémon is primed to be successful in one or two contest types, but may be seen in multiple
After you have completed Master Rank in all Contests, you will get to face Lisia in the Contests, with her Altaria being primed for each type. After that, there is a small chance that her uncle, Wallace, will be in a Master Rank Contest as well.