In cerulean city do not battle the guy on the left of nugget bridge or the boy to the top of the screen by bill's house. Catch a Pokemon with teleport. Go to the boy by nugget bridge from the top. When you are one step away from when he challenges you, hit start and down simultaneously. Teleport back to cerulean and then go to the boy I mentioned second. Teleport again, go up nugget bridge, and the pause screen will come up. Hit b and fight mew!
Mew was originally found in Pokemon red and blue by using the Mew glitch.
blue mew is a shiny version of mew so you have to be very lucky to catch a shiny Pokemon let alone a shiny mew
In the game
Mew was a special event Pokemon that was distributed for Pokemon Red and Blue. Mew cannot be found in the wild without cheats or using glitches, which is still possible to obtain. Bulbapedia likely have a great summary about this Mew glitch in Pokemon Red and Blue.
The Pokemon that are in Pokemon blue are at least the first 149 Pokemon in the pokedex. I'm not sure about Mewtwo or Mew though
Mew i think i have a shiny one its blue :D
The only way to get Mew in Pokemon Red, Blue, and Yellow is via the Mew Glitch, which you can find on Bulbapedia.
(Action replay) You can also use the Mew glitch in Pokemon red or blue and then just trade up.
Anything.
It can be caught in Pokemon blue/red/ and yellow.
you didn´t get mew qith any cheats in ruby =( you can get mew with an mew-glitch in yellow (blue,red) or you can get a mew from my Pokemon ranch for diamant perl and platin but not for ruby the way to get mew in ruby is ... on a Pokemon tour (Pokemon-day ... , ) or with an cheat ... i hope i can help you :-)
Youtube video: "Catching Mew in Pokemon Red and Blue Versions" http://www.youtube.com/watch?v=JkF7Xjxn9jc