|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.
The Second type glitch, also known as the Transform a Water-type Pokémon into Mew glitch is a closed menu Select glitch in Pokémon Red, Green, and Pokémon Blue (Japanese).
It allows the player to transform a Pokémon into another Pokémon with the ID of its second type. As single-typed Pokémon have their second type the same type as the first type internally, they can also be used for the glitch.
Item 13 method (does not always work):
1) Press Select on item 13.
2) Exit with B, B.
3) Open the Pokémon menu via a battle, Day Care on Route 5 or the Name Rater in Lavender Town and press A on the first Pokémon to swap it to be a Pokémon based on its second type.
This glitch may also trigger Pokémon No. 152 in the Pokédex.
Item 14 method:
1) Prepare a party of two Pokémon with the second-type you need.
2) Press Select on item 14.
3) Exit with B, B.
4) Open the Pokémon menu via the Day Care man on Route 5.
5) Press A on Pokémon 1 to swap it with a glitch Pokémon, and then raise and take back Pokémon 1.
6) Repeat steps 2-4 with the other non-glitch Pokémon and then press A on Pokémon 1 to swap it with the desired Pokémon.
|Index number (dec)
||Index number (hex)
||"A" (Japanese 'M (00))
Thanks to Japanese Pokémon select button glitch websites, Meowth346 for discussing this glitch on the Azure Heights forums in 2001, gunbladelad77 for sharing it on GameFAQs in 2009 and then finally ginothepro for uploading footage of it on a real Game Boy in 2012.
The information here is copied from ChickasaurusGL's video with permission. The table is heavily based on Bulbapedia version, also written by Chickasaurus/Torchickens.