mesingo. what????

Messingno....wow. I've done lost of research on him....quiet interesting. He only appears in the original red/blue/yellow/green. (green=japan only.) he is a glitch Pokemon that can appear in several forms. glitch form.(lots of barcodes.)
And any pkmn fossil. (like in the musseum pictures, the bones.)
Or the marwok mom ghost.
You get him:
Talk to the Old Man located North of Viridian City. Allow him to demonstrate how to catch a Pok�mon. Once he is finished, immediately Fly to Cinnabar Island. Make sure that the Rare Candy is in the sixth slot of the bag. Surf up and down along the east coast of the island where the water is touching the land. Whether Missingno. Can be encountered depends on the player's name; other Pok�mon may appear instead. Continue Surfing along the coast until Missingno. Appears (assuming that the player's entered name will cause a Missingno. Encounter). Some names may not cause Missingno. To appear. If so, you may find 'M, which works just as well. Defeat, run from, or catch Missingno. Or 'M. also, look at his name. MissingNo. If tooken apart, it says MISSING NO, or NUMBER because he isnnt a real pokemon. why he's there:
Every Pok�mon has a "Pok�dex byte" that tells the game whether it has been seen or caught. A value of 0 means the Pok�mon hasn't been seen or caught, 128 means it's been seen, and 255 means it's been caught. Missingno.'s Pok�dex byte is in the same location as the byte that stores how many of the 6th item is in the bag, as well as 'M's. This is why, when Missingno. Or 'M is encountered, the sixth item slot is set to 128 (or 255 if it is captured). The glitchy box symbol is a result of the game attempting to display a number greater than 99, which causes it to grab sprites from beyond the number sprites. Sometimes it can appear to be a blank tile, but if you go somewhere else or out of battle it will revert back to an unusual tile. to get him, you must have theese letters in your charecter's name:
G, H, J, M, S, a, b, c, m, o, p, v, w, x, y
Hope I helped! ^ ^

Type it in on google.

Hope this helps,
Nix

He is a glitch Pokemon you do not want to get it will messup your game