More research is needed for this article.
Reason given: Check if the PP Up bonuses are kept in Yellow. Check if a hex:FF can be used to keep the underflowed PP after ending the battle. Check if the Cable Club escape glitch can be used to keep the underflowed PP.
Inconsistency between what moves two games thought Mewtwo used.
The freeze 0 top move selection glitch is a glitch in Pokémon Red, Blue, and Yellow that allows the player to use a move at the top of the fight menu, even if it had 0 PP.
It is one of three known glitches that allow the PP of a move to wrap around from 0 to 63. Others include the Hyper Beam automatic selection glitch and the switch PP underflow glitch.
This glitch is special because it allows the PP of theoretically any valid move to underflow; not just Hyper Beam or a partial trapping move, but since this glitch is only known to happen in a link battle the underflowed PP cannot be kept. However, the full PP Ups effect can be kept in at least Red and Blue.
This glitch also causes a battle to de-sync, like the partial trapping move link battle glitch.
- A slower Pokémon and a faster Pokémon. The slower Pokémon needs to be able to take hits.
- Slower Pokémon: Has a top move with 0 PP and another move.
- Faster Pokémon: Has a Fire-type move and a move that can freeze, i.e. Ice Beam or Blizzard.
- Access to a link battle.
- Any Pokémon that will faint in one hit (may not be necessary).
- Enter the Cable Club Colosseum.
- Have the slower Pokémon select any move. Make sure it doesn't faint the opponent if step 3 fails.
- Have the faster Pokémon use Ice Beam or Blizzard and freeze the slower Pokémon. If the move doesn't freeze, go back to step 2.
- Switch the slower Pokémon for another Pokémon and have it faint from the faster Pokémon's attack.
- Switch the slower Pokémon back in.
- Select fight and have the opponent defrost it with a Fire-type move.
For this article, the side with the slower Pokémon will be referred to as 'player one' and the side with the faster Pokémon will be referred to as 'player two'.
According to player one's side, after the glitch the move selected before the switch will be used, yet the PP of the move at the top of the fight menu will be reduced. On player two's side the game will say that the move at the top of the fight menu was used.
This can lead to a 'desync', which is where both games think different things about the statuses of the Pokémon. If a Pokémon faints on one side but is still active on the other, then an unexpected Pokémon (including glitch Pokémon) may be sent out on the side that the opponent fainted.
PP underflow explanation
If the PP was 0 with no PP Ups applied, it will underflow to 63 with full PP Ups applied. If it was 0 with at least one PP Up applied, it will underflow to 63 with one less PP Up applied.
This is because in Pokémon Red, Blue, and Yellow and Pokémon Gold, Silver and Pokémon Crystal, PP and the amount of PP Ups applied are stored in the same byte. If bit 6 (+40h) is set, then it indicates that one PP Up has been used. If bit 7 (+80h) is set, then it indicates that two PP Ups have been used. If bit 6 and 7 (+C0h) are set, then it indicates that 3 (the maximum amount of) PP Ups have been applied.
Examples: A value of 40h means 0 PP with 1 PP Up applied, a value of 80h means 0 PP with 2 PP Ups applied, and a value of C0h means 0 PP with 3 PP Ups applied. A value of 3Fh means 63 PP with 0 PP Ups applied.
There are only 64 (80h-40h) possible values for PP itself, meaning that the maximum amount of PP is 63.
- For at least two versions of Pokémon Yellow, Haze (a move that can defrost a Pokémon) cannot be used to pull off both the underflow and de-sync parts of this glitch. After Haze is used, player one gets to select a move from the Fight/PkMn/Item/Run box again.