Our rivals have always been trainers, but how do you guys feel about having rival wild Pokémon like pic related?

It could be some rare/strong Pokémon encountered near the beginning of the game on one of the early routes that you can't catch and must defeat. As you make further encounters with it, it starts getting other wild Pokémon to join its team. After you face it for the final time, its group separates and each one can be found in a specific location and caught in an overworld encounter.