Old Man Trick

The Old Man Trick is a glitch that occurs in Pokemon Blue and Red versions. It's the most commonly used method to encounter the glitch Pokemon, Missingno. Since the glitch was patched in Yellow version, a different method is used to encounter the glitch. The player must talk to the old man in Veridian City that teaches the player how to capture Pokemon. During the sequence, the player's name is temporarily changed to "OLD MAN" to show the proper text. However when this happens, after watching the sequence the player must then fly (or teleport) to Cinnabar Island and surf on the coast of Cinnabar. During this time, the player will encounter different Pokemon depending on the route the player was last in. The player will also encounter different glitched Pokemon depending on their name, in which if the player used the correct letters and characters in the proper slots they then will encounter Missingno.

How it Works
When creating the map of which Pokémon appears where, the programmers made a mistake. The strip of land making up the Cinnabar Island Strait was programmed to be a place where wild Pokémon could appear, but they forgot to specify WHICH Pokémon could appear there! Whenever you enter a new area, the data for "What Pokémon appear where" is overwritten with the specific data for that area. However, because no data is specified for the Cinnabar Island Strait, the previous data will remain, enabling you to evidently catch Pokémon there from the last area you visited (this is what causes the Safari Zone trick to take place).

When you watch the Old Man's demonstration, the picture and text change from your name to "Old Man". For this to happen, the programmers changed the variables given to your name so the picture and text can show up as "Old Man". These are stored in the byte containing the data for "What Pokémon appear where" as this was the place the programmers would be a safe place to store them until the demonstration finishes, and they would be overwritten when you entered a new place anyway, but when you go directly from the Old Man's demonstration to the Cinnabar Island Strait, the data won't be overwritten as it should, leaving your name's variables in the "What Pokémon appear where" byte. None of these variable's HEX Values make sense, so it would fit that the Pokémon encountered there would not make sense. The game brings up an empty HEX Value so Missingno appears. (Source: ) In order for the player to encounter Missingno., they must use the following letters in either the third, fifth, or seventh slot in their name. The characters the player should use to encounter "L" Missingno. are: Space,G,H,J,M,S,:,],a,b,c,m,o,p,v for the fossil and ghost type the player must have: w,x,y. (Note: Only characters the player may use without the need of a cheating device is listed, however there are other glitched characters the player can use by means of a cheating device to encounter Missingno.)