Brock

Gym Leader of Pewter City - Rock-type specialist.

Team (Pokemon Yellow):

Reward: Boulder Badge and TM34 Bide.

Badge effect: Boulder Badge raises your Attack by 12.5% and lets you use Flash outside battle.

How to beat him or her: Your starter Pikachu is useless here - Electric does NOTHING to Geodude and Onix because both are part Ground. Yellow deliberately provides two answers on Route 22, reachable before Brock: Mankey learns Low Kick at L9 and Nidoran (M) learns Double Kick at L12, both Yellow-only changes. Butterfree's Confusion at L12 also works.