In Pokémon Blue, your mission is to collect all 150 Pokémon. To collect all 150, you'll need to train each captured Pokémon. Once they evolve, each Pokémon gains power, which can be used to defeat and capture other Pokémon. Along the way, several skilled trainers will challenge you to Pokémon duels. To win the game, you must defeat them all.
Keep in mind that some Pokémon are rare and won't be found in your game. To get all 150, trade Pokémon with your friends using the Game Boy Link Cable, which allows the transfer of Pokémon between Game Paks.