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Stantler. It's like Pokemon Yellow, you don't get a choice. The Stantler follows you around with the sort of amie system Pikachu had, and when Stantler likes you enough, it lets you ride on his back. As the game progresses, Stantler realizes the dex is being cut again because its only like 200 Pokemon big. After you beat the elite four and Stantler realizes there's no national dex, he sacrifices himself in order to create one and all 9999 Pokemon return to the region, except for Stantlers which become extinct.
