Why didn't Leer and Screech work against Giovanni's Kangaskhan? (Gen 1)?

Question

I was playing a Pokemon Blue trashlocke, and I was trying to to a strat against Giovanni's Kangaskhan where I put it to sleep and try to lower it's defense so I can chip it down with Onix to avoid getting it's rage build too high and sweeping my whole team.

However, when I swap into Ekans, everytime I hit leer, it didn't land once. And eventually, Kangaskhan woke up and started to whittle down my team with Rage, before I used Rage myself on Onix and lost the run there due to Kang's rage being built too high.

Am I just unlucky, or is there a reason to why Leer was not landing?

Answer 1

In Gen 1, there is a bug that reduces the accuracy of every move by 1/256. This causes moves with 100 accuracy (like Leer) to effectively have a 99.6% hit rate, making it possible for the move to miss.

Every move has an accuracy value of some number between 0 and 255 inclusive, with 255 representing a move with 100 accuracy. The reason this happens is because the game determines whether a move lands by pseudorandomly generating a number between 0 and 255 and checking if it's strictly less than the move's accuracy value, instead of less than or equal to it. This means that if it generated 255, the move will always miss because 255 is not less than 255.

It is theoretically possible that you just got horribly unlucky. Gen 1 has a lot of bugs and glitches, so it's also possible that something else was the root cause, but it's hard to tell without knowing more about the situation. If you're using a ROM hack for this challenge, that could be a factor too.

There is another separate issue with Leer where it has a 25% chance of failing if used by an opponent outside the Battle Tower, so you may notice that as well.

Source 1 / 2