The following cheats are rated 100+ by my friends, so please rate.
Beat Elite Four and Gary.
Go to Cerlean City.
Cross Nugget Bridge.
Go to the left all the way.
Go down until you see water.
Surf on it.
Go down until you see a cave.
Go to the end and battle Mewtwo.
Do not use a Master Ball.
Get it's HP to RED then use PokéBalls or Ultra Balls.
After the Mewtwo crap, get a National Dex(ALL Pokmemon from Pokemon YELLOW/BLUE/RED and CRYSTAL/GOLD/SILVER)
Go to the Mewtwo Cave.
There is a hidden ladder that is hard to find. You find it bye using Rock Smash on Brownish-Black rocks or walk through the certain ones.(NO GameShark!!!)
You'll see four(4) ladders. Go through the bottom 1st, left 2nd, top 3rd, and right 4th.
You'll see two ladders. Go through the one surrounded by three(3) rocks. You'll see Mew.
USE MASTER BALL WITHIN 5 MINUTES!!!
My little brother figured out the Mew cheat, so it is his credit.
Added by: DarkraiSafari Mar 14th 2008, ID#4820