1/256 miss glitch
The 1/256 miss glitch, also known as the Generation I miss, is a phenomenon in Pokémon Red, Blue, and Yellow where moves that are supposed to have "100%" accuracy actually have a hidden 1/256 chance to miss. The only exceptions to this are moves that bypass the accuracy check altogether, such as Swift or moves under the effect of X Accuracy.
The reason this happens is that the accuracy of a move is stored as a 1-byte integer (i.e. in the range 0–255), where 255 corresponds to 100%. Even when the user's Accuracy stat and the target's Evasion stat are factored in, the calculated probability to hit is still represented as a 1-byte integer (denoted acc below). However, the game then generates a random number rng in the full range 0–255, and the move misses if rng is greater or equal to acc, which means if rng is 255, then the move will miss even if acc is 255 too. In general, this causes the probability of a move hitting to be acc / 256 instead of the more "reasonable" acc / 255.
This glitch is not banned even in "glitchless" speedruns, since it is out of the player's control, and will happen randomly no matter what the player does. Therefore, "glitchless" TASes (which usually follow the same ruleset as RTA runs) can take advantage of Generation I misses for significant time saves, although manipulating such a rare event, especially if it needs to happen together with other rare events (e.g. the enemy's move needs to miss while the player's move needs to critical hit), may cause difficulties even for a TAS. On the other hand, in RTA runs, the player will usually encounter detrimental Generation I misses much more than beneficial ones[note 1], and an untimely Generation I miss can easily kill the run altogether.
| |
See Also
Notes
- ↑ Since overall the player makes more moves than the opponent does!