|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.|
All legitimate Pokémon are obtainable through this glitch, as well as many (if not all) glitch Pokémon from the versions that the glitch is possible.
Though the glitch is normally impossible in Yellow and the English versions, a similar glitch can be ported over to those versions with the international fossil conversion glitch.
Side effectsThis glitch has a bad side effect of changing the player's Fly locations, possibly to a value that freezes the game when the Fly screen is opened, but the player can work around this problem with the right 4th move on the switched valid Pokémon.
Another side effect of the glitch reported is not being able to use Surf, but this effect doesn't always happen. There is no known fix, but the problem can be worked around with by using the ????? (07) item to surf instead of trying to use it from a Pokémon.
ExplanationSee also: Select glitch.
As many select glitches do, the fossil conversion glitch swaps an invalid 'post-6' Pokémon slot with a valid Pokémon (specifically Pokémon #32), putting data into certain unrelated memory addresses based on the data of the Pokémon that was swapped, and putting a glitchy Pokémon that had the data in position 32 in the position where the valid Pokémon was.
Some of the conversions include:
Pokémon's fourth move -> Fly locations byte 1 (D68A) Pokémon's Trainer ID byte 1 -> Fly locations byte 2 (D68B) Pokémon's current experience byte 3 -> Stored fossil Pokémon (D68F)
A Helix Fossil, Dome Fossil or Old Amber in the bag, or stored with the doctor in the Cinnabar Island Pokémon Lab. Access to at least Cinnabar Island. At least 32 items in the items storage box. The valid Pokémon you switch will turn into a glitchy Pokémon, so it is recommended that it isn't valuable. Optional: A chosen current experience modulo 256 value on the valid Pokémon you switch, so you get the Pokémon you want. Optional: A chosen fourth move on the valid Pokémon you switch, so you don't get a fly locations word that freezes the game after opening the Fly menu.
MethodPrepare a Pokémon with a current experience value modulo 256 of the Pokémon of your choice. See the big list and this list for more information. If you need to convert from hexadecimal to decimal, you can use Windows Calculator on 'Programmer' mode.
Also, so that you don't risk getting Fly locations that freeze the game, it's recommended that the Pokémon has one of the following moves in move 4:
01: Pound 03: Doubleslap 07: Fire Punch 0F: Cut 1F: Fury Attack 3F: Hyper Beam 7F: Waterfall
Waterfall (7F), learned by Goldeen at level 37 and Seaking at level 39, is the best valid move, because at worst (with the Player ID byte 1 as 00) only Saffron City, Fuschia City and the Pokémon League are omitted, and at best only Fuschia City is omitted.
Go to the scientist in Cinnabar Lab and choose to resurrect any fossil. Exit the lab but don't re-enter and receive it yet. Go to the PC in Cinnabar Island's Pokémon Center and access the Items Storage System. Use the select button on the 32nd PC item, and exit with B, B. Go to the Pokémon Mansion and encounter any Pokémon. Within the battle, go to the Pokémon screen and select any Pokémon. After choosing the 'RUN' option, if the player returns to the scientist and receives his or her Pokémon they will notice it has become another Pokémon. The Pokémon has an index number equal to the total experience (modulo 256) of the valid shifted Pokémon.
A step by step guide of the fossil conversion glitch for Pokémon Red and Green in Japanese.