The Missingno. Cheat
To get Missingno. And other high level Pok�mon depending on your name talk to the guy in Viridian City (the one who has just had his coffee) and watch him catch the Weedle. Fly to Cinnabar Island and Surf along the east coast until you encounter a Pok�mon. It will most likely be Missingno. (beware of 'M!) but it might be a really high level Pok�mon (over level 100) depending on your name.
More tricks, tips and cheats for this game are right here - Pokemon Blue cheats
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