Pokémon Red and Blue/Vermilion City

Do some Pokémon Trading
The trader won't deal with Yellow players, but they can talk to the policewoman just outside for a free once they've won the Thunder Badge. She is hoping that you will take good care of it. It's only Level 10, so it'll take a while to train, but you won't get many other Water-types for a while.

Red/Blue players can trade a for a one-of-a-kind  in the building above and to the right of the Gym. Don't hesitate to make this trade if you have an extra Spearow! If you don't have a Spearow to spare, you'll get a chance to grab one in the upcoming Route #11.

Many important items
Convince the man in the building west of the Pokémon Center that you love fishing as much as he does and he'll take a shine to you. He will give you his Old Rod as a gift! Now you can use it near any body of water and get... a. Or... another Magikarp. Yes, that's all this rod catches. Good news if you didn't buy one earlier.

Something slightly cooler than the Magikarp Stick can be found at the Pokémon Fan Club, located directly above the Gym. Listen to the president's boring story and he'll give you his Bike Voucher. Redeem it at the Bike Shop in Cerulean City, and you'll get a Bicycle that you can use anywhere to increase your movement speed.



Trainer Battle 3: Lt. SURGE


Use HM01 Cut (obtained after the events on SS. Anne) to hack down a bush and reach the Vermilion City Gym entrance. Once inside, you'll be confronted by a few trainers and a double-locked door. To reach Lt. Surge, you'll have to find the two switches hidden in the trash cans on the floor. The switches are randomly located, but once you find one, the second will be right next to it. If you don't get it on your first try, the switches will move and you'll have to search again.

Surge's is certainly a dangerous opponent, but Ground-type Pokémon like  and  are completely immune to its Electric attacks (and the former resists its Normal-type moves as well), and your Electric and Grass Pokémon resist them. For offense you can use your own Ground-type attack, Dig, for devastating results. With any luck, you caught a Geodude or two back at Mt. Moon. If you didn't, make a detour down by Route #11 into Diglett's Cave. There, you can capture some and  to even out the odds with Lt. Surge. Otherwise, stick with regular attacks, as long as they aren't Flying- or Electric-type.

Your prizes include the Thunder Badge and TM24, which can teach the powerful Electric-type attack Thunderbolt to a variety of Pokémon. This includes Pikachu, although in the Yellow version it'll learn it by itself at level 26, so you may want to use it on something else, or save it for another Electric Pokémon.