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I was looking at the Bulbapedia oage for the Sinnoh League, and I had a thought:
In Diamond and Pearl, only two of Flint's Pokémon are Fire-Type, yet he is still classified as a Fire-Type specialist. Additionally, Cynthia's team carries both two Water-Types (Gastrodon and Milotic) and two Ground-Types (Gastrodon and Garchomp). Technically, applying the standard set by Flint, one could classify Cynthia as either a Water-Type or a Ground-Type trainer.
Thus, I built two teams for this hypothetical scenario. One mono-Water and one mono-Ground.