Pokémon Red and Blue/Mew glitch

, the secret 151st Pokémon is so rare that you won't be able to find it in your game in any conventional manner. While you can still get credit for filling your Pokédex without it, it's a great Pokémon that you probably won't want to miss.

So how do you get it? Thousands of lucky trainers were given Mews by bringing their Game Boys and Pokémon Game Paks (of any version) to various Nintendo Power events, such as their various Mall Tours, where a Mew was given to them for free. If you missed out on those events, you would be out of luck since Nintendo no longer gives first generation Mews away anymore. Codes for cheating devices such as Game Sharks were developed, but they exposed your game's save file to the risk of being corrupted or erased. These were your only options originally. That is… until now.

Clever unconventional players have discovered that it is possible to obtain the rarest Pokémon in Red/Blue/Yellow,, without using a cheating device. Players have learned how to exploit a bug in the program that allows you to encounter any Pokémon that you would like, and you can use this method to obtain a Mew for yourself. It's not too difficult, but it's a good idea to save before you try this so that you can start over in case you make a mistake.

There are two primary ways to activate this glitch. No matter which method you choose, you must not defeat the Youngster with the Level 17 Slowpoke on Route #25 (marked #4 on the Route #25 map).

Method 1
The first method is at the earliest point in the game during which this glitch can be performed. It would be a good idea to have open spaces in your party, as sometimes the game may freeze when you try to withdraw Mew from the PC. Make sure you also have something other than a normal Poké Ball to catch him with, as these are sometimes not strong enough. As you progress through the steps, you'll realize you will also need an Abra. And seeing as the Mew is at level 7, you better have something with a low enough level that it won't kill the mew on the first move.
 * 1) Fight your way through all of the challengers on Nugget Bridge.
 * 2) Catch an any way that you can, but don't engage the Jr. Trainer (Marked #7) who hides in the grass on the left of Route #24. This will come later.
 * 3) Place Abra in your party if it's not already.
 * 4) Make your way towards that Jr. Trainer, marked #7 on the map on Route #24. He's the one that says "I saw your feat from the grass" when he challenges you.
 * 5) *Save the game at this point.
 * 6) Stand in front of the Jr. Trainer, just outside of his sight. Move down until he sees you.  As soon as he does, immediately press . The exclamation point will not be above his head yet, not until actually Teleporting.
 * 7) Select your Abra and use Teleport. If you did it correctly, the trainer should have an exclamation point above his head as you Teleport.
 * 8) For the time being, your menu will not work. This is normal.  Proceed to Route #25.
 * 9) Approach the Youngster (#4) on Route #25, but do not battle or talk to anyone else besides the one Mountain Man (#1). You must battle him from as far away as possible. It is impossible to avoid him, but it will still work if you then head to #4. [After fighting the Mountain Man your start menu will be accessible again, but it is not recommended to access it as it is unknown what may go wrong here. Same goes for the Youngster.]
 * 10) You must engage the Youngster in battle from far away. Do not walk towards him and talk to him or the game will freeze.
 * 11) Battle the Youngster and defeat his Slowpoke.
 * 12) Now walk back to Route #24. As soon as you reach the route, your Start menu will automatically appear.
 * 13) Press to cancel the menu, and you will instantly be taken to a battle with a level 7 Mew.
 * 14) Weaken the Mew enough to catch it, and it's yours. Normal Poké Balls will not always work though, so try something stronger.
 * 15) If fighting Misty is postponed, the Swimmer in the Cerulean City Gym may be used just as the Youngster, without requiring fighting the Mountain Man. After defeating the Swimmer, walking north to the Nugget Bridge will trigger the appearance of Mew as before. Since the Jr. Trainer never has to be battled, you can catch two Mews this way before ever seeing Misty or Bill.

Warning: Do not talk to anyone in Cerulean. Doing so may trigger glitch battles, slowdown, and game crashes.

Also, you can try a newly discovered method to get an early. It is similar to this method, but the result is different:

Do the first method, but only the first part (going away from the Jr. Trainer). Then take the underground path by going through the house, not talking to anyone. Now go through the path and when you emerge, battle the first bug catcher from as far as possible. Make sure you haven't battled him yet (just like you haven't battled the youngster). Then poison one of your Pokémon in the battle but still be able to defeat him. After defeating him, go through the underground path once more. When you emerge, enter Cerulean by going through the house. Before that your poisoned Pokémon must have fainted. Now go up the Nugget Bridge and you'll see a replacement for the menu: another warning that your Pokémon fainted again. As always, cancel it with and you'll battle a level 7 Grimer.

Also you can use this method to get a nidoqueen if you do the exact same steps but go to the other youngster on route 25 instead.

Method 2
The second method can only be done later in the game because it requires that you obtain HM 02 which contains Fly, from Route #16.
 * 1) Fight your way through all of the challengers on Nugget Bridge. You must be able to approach the Youngster on Route #25 without interruption.
 * 2) Go to the Underground Tunnel entrance to the east of Saffron City. Make sure that you have a Pokémon with the Fly ability.
 * 3) *Save the game at this point.
 * 4) Approach the Gambler (#8 on the map) from the north. Stand in front of him, just outside of his sight.
 * 5) Move down until the Gambler sees you. As soon as he does, immediately press.
 * 6) Select the Pokémon who knows Fly and head to Cerulean City. If you did it correctly, the trainer should have an exclamation point above his head as you Fly away.
 * 7) For the time being, your menu will not work. This is normal.  Proceed to Route #25.
 * 8) Approach the Youngster (#4) on Route #25, but do not battle or talk to anyone else.
 * 9) You must engage the Youngster in battle from far away. Do not walk towards him and talk to him or the game will freeze.
 * 10) Battle the Youngster and defeat his Slowpoke.
 * 11) Now fly to Lavender Town. Head west back to Route #8.  As soon as you reach the route, your Start menu will automatically appear.
 * 12) Press to cancel the menu, and you will instantly be taken to a battle with a level 7 Mew.
 * 13) Weaken the Mew enough to catch it, and it's yours.

You can also do this glitch battling other trainers besides the Youngster. Each trainer results in different Pokémon, just like Mew, at level 7. You can get other rare Pokémon this way.

Warning: Do not talk to the ghost girl in Lavender. Doing so will trigger a glitch battle, slowdown, and game crashes.