The MissingNo (short for "Missing Number") glitch is one of the most famous glitches in the Pokémon series, particularly in Pokémon Red and Blue versions for the Game Boy. Below are the steps to encounter MissingNo, but it's important to approach this glitch with caution as it can potentially corrupt your game data. 1. **Talk to the Old Man in Viridian City**: Start off by visiting Viridian City and speak to the elderly man who teaches you how to catch Pokémon. When he asks you if you are in a hurry, respond with "No". After you watch his demonstration of how to catch a Pokémon, the glitch setup is initiated. 2. **Fly to Cinnabar Island**: Immediately after the demonstration, use the Fly ability to travel to Cinnabar Island, located on the southeast side of the Kanto region. 3. **Surf Along the East Coast**: Once you arrive at Cinnabar Island, use the HM Surf to ride a Pokémon along the east coast of the island. Be sure to stay adjacent to the land, as MissingNo appears in the areas where the land meets the water. 4. **Encounter MissingNo**: While you're surfing up and down the coastline, you will eventually encounter wild Pokémon. Due to the earlier manipulation with the old man, the game's memory is now confused about which Pokémon should appear in this area, leading to the encounter with MissingNo or other glitched Pokémon. 5. **Catch or Defeat MissingNo**: You can choose to catch MissingNo, but be aware that doing so may cause graphical anomalies or other unpredictable behavior in your game. Alternatively, you can defeat or flee from it. Encountering MissingNo can also result in the item in the sixth slot of your inventory being duplicated to 128 due to an overflow glitch. This glitch can be performed as many times as you like, and it's often used for item duplication. MissingNo itself is not a true Pokémon, so it won't appear in the Pokédex. The glitch is known to not majorly harm your game, but it can lead to graphical bugs, and in rare cases, it may corrupt your save file..sprites. It's a glitch associated with the way the game reads data, not an intentional design by the developers. As a cautionary note, if you're playing on a treasured save file or in an official setting, it might be best to avoid such exploits. The MissingNo glitch is primarily a curiosity from the early days of Pokémon gaming and is not necessary for completing the game or enjoying the Pokémon experience. Also, it's worth noting that the MissingNo glitch was not officially designed into the game; it's a product of oversight in the game's coding. Due to this, later versions of Pokémon games, such as the FireRed and LeafGreen remakes, do not have this glitch. Each game comes with its own set of bugs and glitches, with some having been patched out in later releases or in re-releases on platforms like the Nintendo 3DS Virtual Console.