The second Gym Leader you will face on the road to collecting all eight Kanto Gym Badges is Misty. She is the Cerulean City Gym Leader, specializing in Water Type Pokemon. Because Misty is faced so early in your journey, her Pokemon Team won't be all that difficult to defeat regardless of the Starter Pokemon you selected. However, if you did pick Bulbasaur as your Starter Pokemon, you will have the clear advantage over Misty since she is especially weak against Grass Types.
If you happened to choose Charmander or Bulbasaur as your Starter Pokemon, you will probably need to add an additional Pokemon on your way to Cerulean City to better help you with Misty's Staryu and Starmie. The best Pokemon for this job is Pikachu, which can be found in Viridian Forest just north of Viridian City and Route 2. In addition to being weak against Grass Types, Misty's Water Type Pokemon are also weak against Electric Types like Pikachu.
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