Uploaded November 2014 | Updated September 2026, 3 weeks ago
Short version:
In Pokemon Red, Blue and Yellow, if a Pokemon with a Defense or Special stat of 512 or 513 uses Reflect or Light Screen (respectively), the game will freeze upon the Pokemon being attacked with a physical or a special attack, respectively.
In addition, if a Pokemon with a Defense or a Special stat of at least 514 uses Reflect or Light (respectively) its stat will be treated as if it was much lower during damage calculation.
Long version:
Prior to damage calculation, if either the attacker's Attack/Special stat or the defender's Defense/Special stat is 256 or higher, both stats are temporarily quartered so that the stat values can fit in one byte (0 - 255). This assumes that stats can never be higher than 256*4-1 = 1023. While this is still mostly true because stats cap at 999, it doesn't account for the fact that Reflect or Light Screen temporarily double the stat ignoring that cap, allowing a stat to become up to as high as 999*2 = 1998 during damage calculation.
A stat that is exactly 512 or 513 prior to the use of Reflect or Light Screen will become 1024 or 1026 respectively afterwards. When 1024 or 1026 is quartered (and floored), it becomes 256. 256 in binary is 100000000, so if we ignore the 9th bit (in order to fit the number in one byte) it becomes 00000000 or simply 0. When the game attepts to divide by the Defense/Special during damage calculation, it's going to be attepmting to divide by 0. The game will go into and endless loop trying to divide by 0, so everything but the music will freeze.
A similar thing occurs for stats between 514 and 999. The game won't freeze, as the stat will not become 0, but the stat will be effectively treated as if it was much lower (e.g. 514 and 515 will become 1, 516 and 517 will become 2...).
Short version:
In Pokemon Red, Blue and Yellow, if a Pokemon with a Defense or Special stat of 512 or 513 uses Reflect or Light Screen (respectively), the game will freeze upon the Pokemon being attacked with a physical or a special attack, respectively.
In addition, if a Pokemon with a Defense or a Special stat of at least 514 uses Reflect or Light (respectively) its stat will be treated as if it was much lower during damage calculation.
Long version:
Prior to damage calculation, if either the attacker's Attack/Special stat or the defender's Defense/Special stat is 256 or higher, both stats are temporarily quartered so that the stat values can fit in one byte (0 - 255). This assumes that stats can never be higher than 256*4-1 = 1023. While this is still mostly true because stats cap at 999, it doesn't account for the fact that Reflect or Light Screen temporarily double the stat ignoring that cap, allowing a stat to become up to as high as 999*2 = 1998 during damage calculation.
A stat that is exactly 512 or 513 prior to the use of Reflect or Light Screen will become 1024 or 1026 respectively afterwards. When 1024 or 1026 is quartered (and floored), it becomes 256. 256 in binary is 100000000, so if we ignore the 9th bit (in order to fit the number in one byte) it becomes 00000000 or simply 0. When the game attepts to divide by the Defense/Special during damage calculation, it's going to be attepmting to divide by 0. The game will go into and endless loop trying to divide by 0, so everything but the music will freeze.
A similar thing occurs for stats between 514 and 999. The game won't freeze, as the stat will not become 0, but the stat will be effectively treated as if it was much lower (e.g. 514 and 515 will become 1, 516 and 517 will become 2...).
