From Glitch City Laboratories
Within Pokémon Red, Blue and Yellow one particular byte corresponds to what type of battle system the game will use when the player encounters a wild Pokémon. These normally include battle systems such as a normal wild Pokémon battle, the battle system used in the Safari Zone and the Old Man attempting to catch a Pokémon, however there are a number of glitch battle systems within the game, but only two are known to have unique effects.
Battle system #4 (03) (Pokémon Red/Blue only)
This battle system has the equivalent hexadecimal identifier to an existing unused battle system in Pokémon Yellow in which the player cannot make a move because it will display the message "Hurry, get away!". However the effects of its Pokémon Red and Blue equivalent appear to be purely glitch or as a value to account for coding elsewhere. When encountering a wild Pokémon it will appear at level 0 by default which may suggest that it is reading data from another byte than the ordinary one which reads the Pokémon's level. When 'FIGHT' is chosen the battle will suddenly end but then instantly start again. This is also the case for other battle options for example if 'item' is chosen the battle will suddenly end after an item is used. Like its Pokémon Yellow equivalent the player will not send out any Pokémon and instead the player's battle sprite for trainer battles will remain on the screen.
Battle systems #5 (04) up to #255 (FF) (starting from #6 in Pokémon Yellow)
The rest of the slots corresponding to unused battle systems share the same effect. For these battles when the player attempts to choose 'RUN' the game will always display 'Can't escape.' Like the fourth battle system on both games the player will not send out any Pokémon and will keep the normal trainer battle sprite throughout the rest of the battle. When the player selects 'FIGHT' nothing will happen as although the normal selection sound is made the game will not progress to the move selection screen.
- Unused battle system (Yellow)