A Mew from the expanded party after the 255 Pokémon glitch.
This article details how to obtain Mew in the expanded party with the 255 Pokémon glitch.
The 255 Pokémon glitch (see also SRAM glitch) involves resetting Pokémon Red, Blue or Yellow early after choosing to save at a specific time shortly after the Yes/No box disappears.
This gives the player a party of 255 Pokémon. One of the Pokémon (such as the first or second) can be swapped with the tenth to obtain an expanded items pack of 255 items.
With the following steps for Pokémon Yellow, you can find Mew:
1) Perform the SRAM glitch.
2) Swap Pokémon 2 with Pokémon 10.
3) Walk outside to Pallet Town and find Rare Candies hidden deep in the expanded items pack.
4) Use them on Pokémon 1 until Pokémon 1 is level 5.
5) Pokémon 10 now has Mew's sprite. But if you obtain a Pokémon from Professor Oak, it may no longer have Mew's sprite for some reason.
Items past slot 20 and Pokémon beyond slot 6 both have extrapolated data, and their addresses typically represent unrelated variables that may have already been reserved for something else; so changing the data of them can cause an effect, like how altering the quantity of item 36 affects the exit destination for certain maps.
The Pokémon species byte 1 list is stored like this:
- D163 - # Pokémon In Party
- D164 - Pokémon 1
- D165 - Pokémon 2
- D166 - Pokémon 3
- D167 - Pokémon 4
- D168 - Pokémon 5
- D169 - Pokémon 6
- D16A - End of list
(All of the addresses in this region are -1 in Yellow, and other addresses can be found in the Pokémon Red and Blue RAM map on Datacrystal)
The addresses for other Pokémon carry on as expected (by +1). This means that Pokémon 8 takes its Pokémon species byte 1 data from D16B (D16A in Yellow), which is already reserved for the second (usually identical) species byte of Pokémon 1.
Pokémon 10's species byte 1 is D16D (D16C in Yellow); the least significant HP byte.
Coincidentally, you can make Pokémon 1's HP equate to 21 with the Rare Candies (item 79 represents a Rare Candy when you are outside in Pallet Town). This is equal to Mew's index number (see The Big HEX List); hence it makes Pokémon 10 appear as Mew.
You cannot use the exact same steps in Pokémon Red and Blue, probably because the hex:FF glitch Pokémon ('M (FF) and Q FF)) have different base stats between Red, Blue and Yellow. However, a method of finding Mew at the beginning of the game is theoretically possible.
- ChickasaurusGL (documentation, article text with permission)