Lt. Surge is the Electric-type Gym Leader. His team consists of a Level 21 Voltorb, a Level 18 Pikachu, and a Level 24 Raichu. All are weak to Ground-type moves. Catching a Diglett or Dugtrio in Diglett's Cave (east of Vermilion City) is highly recommended, as they are fast and have strong Ground-type attacks. If you chose Charmander, its evolutions will struggle here. Be wary of Raichu's speed and powerful Electric attacks. Use Ground-types to absorb damage and retaliate.
