Here's how to get it:
1. Beat the Vermilion City Gym. This gym focuses on Electric-type Pokemon, so bring Pokemon that resist electric attacks (Ground, Grass, and Flying types are good options). You can also use Pokemon that are strong against Electric types.
2. Challenge Lt. Surge. After beating the gym trainers, you'll face Lt. Surge himself. He has a level 29 Raichu, a level 27 Voltorb, and a level 27 Magnemite. Use your strategy to defeat his team.
Once you defeat Lt. Surge, he will award you the Thunder Badge. This badge gives your Pokemon the ability to learn the Thunder move and allows you to use Fly outside of battle.
Some tips for defeating Lt. Surge:
* Use Ground-type Pokemon: Ground-type Pokemon are super effective against Electric-type Pokemon. Try using a Golem or Rhyhorn.
* Use Grass-type Pokemon: Grass-type Pokemon are also strong against Electric-type Pokemon. Try using a Bulbasaur, Oddish, or Gloom.
* Use Flying-type Pokemon: Flying-type Pokemon are resistant to Electric-type attacks. Try using a Pidgeotto or Pidgeot.
* Use status moves: Moves like Thunder Wave can paralyze Electric-type Pokemon, making them less effective in battle.
Good luck getting the Thunder Badge!