Pokémon FireRed and LeafGreen/Celadon City

Celadon City is the largest city in this game. Its Poké Mart has six stories; no wonder it needs an elevator! They sell all sorts of things. You'll be able to buy TMs and normal items (such as Potion and Antidotes) on the second floor. On the third floor, you'll see many people playing Game Boy Advances. Talk to the person at the register, a Move Tutor, and he'll teach one of your Pokémon the move Counter. The fourth floor has many evolution stones you can buy to evolve certain of Pokémon (ex. Eevee) for $2100 each. On the fifth floor, you'll be able to buy items such as X Attack and Calcium. These are items that modify a Pokémon's stats so they can do better in battle. Finally, you'll reach the rooftop, where you'll find three vending machines and two people, including a little girl. Get a Fresh Water, a Soda Pop, and a Lemonade from the vending machine, and give it to the little girl one at a time. She'll give you TM16 - Light Screen, TM20 - Safeguard, and TM33 - Reflect, respectively, for your drinks.

Celadon Mansion
There is a huge building to the right of the department store that's nearly empty inside. Talk to the old lady who's surrounded by Pokémon on the first floor. She'll give you Tea, which you can give to any one of the Saffron City guards so they can let you through. You'll also find the game's programmers in this building, one of which will tell you to return after getting all the Pokémon. He'll give you a diploma for catching all the Pokémon.

Now leave the mansion, and go in through the back door. Go all the way to the rooftop, where you'll find a small building. Inside you'll find a person and a Poké Ball on the table. Pick it up; it's an Eevee!

Other Stuff
The restaurant south of the Game Corner has a man who'll give you a Coin Case to carry your coins. There is an old man to the left of the Game Corner, and can be reached only by surfing across the water. He's a Move Tutor, and can teach your Pokémon Softboiled.

While you're in town, you can pick up HM02 - Fly early. Head west to route 16, use cut on the small tree, and go through, continuing west. Stay to the bottom if you don't want to be challenged by the couple, who will dual-battle you with a level 29 Rapidash and a level 29 Ninetales. See Route 16-18 for image.

Game Corner
Now go to the Game Corner, a place full of slot machines and people on them. Team Rocket made it, and you win or buy coins in order to trade it in for Pokémon and TMs in the building to the right of the Game Corner. A few people will give you free coins, and there are invisible coins scattered on the ground that you can pick up. At the top of the Game Corner, battle the Rocket member, and push the button on the poster. A staircase leading to the basement appears. See Rocket Hideout for the walkthrough.

Gym Battle
After beating Giovanni in the Game Corner, head to the gym by cutting the tree. Here you will battle Erika and other trainers. Erika is the trainer in the middle between the two trainers inside the enclosed area. Beating her grants you the ability for all pokemon up to lvl 50 to obey and earns you TM19 - Giga Drain and the Rainbow Badge!

Leader
Fire and flying are both super effective against grass. A high level Charmelon or Pidgeotto will make quick work of Erika, especially if you picked up Fly beforehand. Vileplume knows both poison and stun powder, so respond in kind by stocking antidotes and paralyze heals.

Items

 * take path next to Pokemon Center
 * use same path and enter building, go to roof
 * PP Up: hidden east of a tree that can be cut, east of the Game Corner
 * 10 coins: hidden near the northwest of the entrance of the Game Corner, below the machines
 * 10 coins: hidden near the northeast of the entrance of the Game Corner, below the machines
 * 10 Coins: hidden in the west aisle of the Game Corner, found a step behind where the woman is sitting
 * 20 Coins: hidden in the southwest corner of the Game Corner, found on the ground near the end of the left aisle
 * 10 Coins: hidden in the middle aisle of the Game Corner, directly behind where the elderly man is sitting
 * 20 Coins: hidden near the middle aisle of the Game Corner, around the ground near the top left seat
 * 10 Coins: hidden near the northwest corner of the Game Corner, found around the left side of the counter
 * 10 Coins: hidden near the right side of the counter in the Game Corner
 * 10 Coins: hidden near the northeast corner of the Game Corner, on the ground in front of the wall separating the stairs
 * 40 Coins: hidden near the northeast corner of the Game Corner, on the ground between the wall separating the stairs and a slot machine
 * 100 Coins: hidden near the southeast corner of the Game Corner, a step away from the Printer