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The player encounters one of several glitch Trainers
which can trigger the ZZAZZ glitch.
The ZZAZZ glitch is a glitch found in the Generation I games. It can be encountered by using the Ditto glitch with a Special stat that has a decimal number of any multiple of 251, 252, 254 or 255. This makes the player encounter a glitch Trainer that in turn allows this glitch to occur.
This Trainer can be difficult to beat particularly due to the fact that the HP bar of the first Pokémon is abnormally high similar to the side-effects of using a Super Glitch move.
The first of the opponent's Pokémon is usually level 153, proving to be more difficult to beat than a normal level 100 Pokémon. Strangely, the player can easily escape this Trainer by using an item such as a Poké Ball or Poké Flute, regardless of the fact in a normal battle this would normally have no effect. The glitch Trainer usually has a 'M (FF) or a Q◣ in his first slot; depending on whether the version is Pokémon Red and Blue or Pokémon Yellow. This Trainer will usually block a thrown Poké Ball however, the battle would suddenly end.
A side effect of the ZZAZZ glitch causes the player's name to become replaced with one that is much longer, causing most previous letters in the player's name to be replaced by 'Z's.
Another notable side-effect of this glitch is how it changes the Pokémon in the Trainer's party to level 153. Most sprites of Pokémon in the party are replaced with the back-sprite of Bulbasaur and outside of battle the Trainer's sprite changes on the Trainer Card. A possible explanation to why the back-sprites of all of the player's Pokémon in battle are changed to Bulbasaur is because the ZZAZZ glitch overwrites several variables with the hex value 99. This explains why the party Pokémon are changed to level 153 because a hexadecimal value of 99 is equal to the integer 153 in standard decimal. A hexadecimal value of 99 also corresponds to the letter 'Z' and the move 'Explosion,' which suggests that the ZZAZZ glitch has made a significant change to the data of the party Pokémon. Other less noticeable effects include changes to the interfaces in-game such as the menu, where if a player attempts to save the game the cursor scrolls over 'yes' and 'no' causing the game to crash. A white screen will appear if the player attempts to view their party Pokémon.
Although the player's name will glitch, the OT values of the party Pokémon will stay the same. This 'tricks' the game into thinking that they are not the player's Pokémon. The combination of this, and the Pokémon's levels being at 153, causes them to disobey the Trainer (as not even the Earth Badge is programmed to make Pokémon over level 100 obey the player.)
Any Trainer battle fought during the glitch will become a battle against a glitch Trainer with the player's sprite. He will either borrow the player's original name, their ZZAZZ-glitched name, or sometimes a different glitched name. His party will consist mainly of several 'M (FF) or Q◣, and this Trainer could be considered 'almost impossible' to defeat, because one of his 'M (FF)s has an extremely large amount of HP that is possibly close to the largest maximum amount of a Pokémon when taking two bytes into account (65535).
If the player saves after activating the ZZAZZ glitch, their save file will be corrupted and they will be forced to start a new save file.
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*Indicates glitches which have been officially acknowledged