Vaporeon

Vaporeon was a mediocre defensive Pokemon outclassed by Suicune for the majority of GSC's history. Its draws over Suicune were access to Reflect and Haze, but ultimately not having that monstrous Defense stat left it unused in OU. Then, the NYPC gods gave Vaporeon and its Eeveelution brethren a gift from Pokemon heaven—Growth—which catapulted Vaporeon into legitimate OU territory. Growth is the only move in GSC that boosts the Special Attack stat, and Vaporeon is by far the best user for a standalone special sweep thanks to its bulk and high Special Attack. Nowadays, while Vaporeon still has the same defensive prowess, Growth boosts its Special Attack, which is high even without a boost but often overlooked, and makes it one of the premier offensive threats in the game. Vaporeon is a threat that must not be underestimated despite its initial lack of popularity.