Old Man Glitch
In order to perform the Old Man Glitch, go to Veridian City and talk to the old man. Say no when he asks you if you are in a hurry and he will teach you how to catch Pokemon. After watching his demonstration, Fly to Cinnabar Island and Surf on the east coast. The Pokemon you encounter are based on the characters in your name. Commonly, you can encounter 'M or MISSINGNO.