Encounter table manipulation Select glitch (Red/Green/Blue)

Please note that this glitch only exists in the Japanese versions of the game, or is otherwise a glitch from a Pokémon game which was only released in Japan.

Using a closed menu Select glitch in Pokémon Red, Green, and Pokémon Blue (Japanese), it is possible to manipulate the encounter table to match data based on the Pokémon swapped with Pokémon 40. This can be done to manipulate at least two encounters.

Since this is refreshed after every battle, the Select glitch must be set up still on the overworld, using an NPC whom brings up the party menu (the Lavender Town Name Rater or Day Care man). Cave encounters apply so no grass tiles are needed.

Requirements

• Expanded inventory or a PC storage box with at least 40 items

Steps

The following is an example method tested on Japanese Red v1.0:

1. Go to the Name Rater's house in Lavender Town. (If using PC storage box, go to the Pokémon Center to press Select on storage box item 40 first)
2. Do a Select glitch with item 40 on the desired party Pokémon. (If Cancel, erase it using a x255 stack directly below it. If the game freezes, try the Select glitch freeze workaround)
3. Save the game and walk around to encounter a Pokémon while still in the house. Reset if the desired Pokémon isn't found and walk around again.

Conversion

Assuming the swap is done on Pokémon 1;

• 1st Pokémon Defense Byte 2 becomes the grass/cave encounter rate ;D152>D806

• 1st Pokémon Speed Byte 1 becomes the first level slot ;D153>D807
• 1st Pokémon Speed Byte 2 becomes the first encounter slot (species) ;D154>D808

• 1st Pokémon Special Byte 1 becomes the second level slot ;D155>D809
• 1st Pokémon Special Byte 2 becomes the second encounter slot (species) ;D156>D80A

Ideally the Defense of Pokémon 1 should be not too low, while the Speed and Special can be used to match a Pokémon with the ID desired by the player.