Red/Blue - Cheats
Can Mew really be obtained without a code or a giveaway from Nintendo? Yes, it can. In order for this ultimate cheat to work, you need to view the requirements below. They are very important; missing one will cause the cheat to not work! Follow this guide exactly the way it's written. Everything done here is an important step, and must be done correctly. This cheat works for Red, Blue, and Yellow.
1. Have at least three badges
2. Have HM 02 - Fly taught to one of your Pokemon
3. Have not battled the Gambler with two Poliwag and Poliwhirl on Route 8 and the Youngster on Route 25 (near Bill's house), who has Slowpoke.
If you meet these requirements, then it's time to catch Mew. First, you'll need to go to Route 8, and stand by the door that leads to the Underground Path. Save right here. You may not save again, or this cheat won't work. Walk one step foward towards the Gambler, and press the Start button immediately. If, however, he challenges you to a match, turn off the game and do it over. The start menu will pop up, and you'll be facing the Gambler. Choose one of your Pokemon and fly to Cerulean City. As you Fly, the Gambler will notice you, and the familiar ! will pop up on his head. The Start button won't work for a while.
Go across Nugget Bridge and head towards the Youngster found among the bushes. He is facing upwards, and when you walk towards him, you want him to walk facing up to you. Defeat his Slowpoke, and fly to Lavendar Town. Go west on Route 8, and the Start menu will pop up by itself. Press B. Mew will appear. Good luck on catching it!
Duplicate Items Code
First put the item you want duplicated (or 99-plicated) in the sixth slot in your items. Talk to the old man in Viridian City. Say NO to his question. Then fly to Cinnabar island, and surf on the right coast. Soon, you'll be meeting Pokemon over level 100. When you meet MISSINGNO., defeat or catch it. After that, you should have over 99 of the item.
WARNING! MISSINGNO. is extremely dangerous. If you meet MISSINGNO. during the game, it can ruin your game. Use this cheat at your own risk.
Here's a good cheat to let you use Pokeballs as Masterballs:
Throw out a Pokeball at a Pokemon. Once it's in the air, hold down "B" and the down or up button. This code cannot be used forever. "Up B" and "Down B" each can be used only 3 times.
Set up a trade with the game link cable. Make sure one Gameboy has a Pokemon that will not matter if it is deleted. This would mean Magikarp, Ratatta, etc.
When the person with the good Pokemon, such as Mew or the Legendary Birds, screen says "Waiting...!" there will be a very small pause. The person with the good Pokemon should shut off his Gameboy instantly at this time. The other person may now turn off his Gameboy.
If you did the code correctly, when the game is turned back on, both people will have the good Pokemon.