The Mew Glitch is a Glitch in the Generation I games. It allows players to catch many normal and Glitch Pokemon, mostly Mew, and can be used without having to own a Gameshark or other cheating device. It has three methods of use.
To capture Mew as early as possible the player must not have defeated the junior trainer on Nugget Bridge or the Swimmer Boy in Cerulean City Gym. The player must also have a teleprting Abra. You should have some Pokeballs stocked up first. First the player heals at the Cerulean City Pokemon Center. The player must then stand over the junior trainer so he is just off the screen. The player must start going down until you are seen. When you are seen immediately press Start. Then use teleport with Abra. If done correctly while the player is teleporting the exclamation point should appear over the junior trainers head. The player must then head east into the Cerulean City Gym and battle the Swimmer Boy. The player must then head back to Nugget Bridge. After a few steps the Start Menu will appear. After closing it the player will begin battle with a LVL 7 Mew.
Note: Mew will always appear regardless of the Special Stat of the last Pokemon Captured.
In Method 2 the player must go see the Gambler in Saffron City. Stand above him so he is just offscreen. The player must then take one step down without the Gambler seeing them and immediately press Start. The player must then Fly to Cerulean City. The player must go to Route 24 and battle the youngster with a Slowpoke. After battling him the player must Fly to Lavender Town. Then head towards Route 8. The Start Menu will appear, press B and a battle will begin with a LVL 7 Mew.
Could someone else post this method. I don't know it.