>>32746108>>32746112It's a myth. It would require the Pokemon to have a catch rate of 1 or 2, which doesn't exist. Hence why there's no real evidence of it happening -- it's all bad theory.
However, it can happen in Gens III & IV
This is due to a glitch in the catch rate calculation, so it has nothing to do the Pokemon you are trying to catch, its current HP, or any other factor. The error is due to the use of a ≥ instead of a >.
In order to catch a Pokemon, the game performs four separate checks. In any situation where you ought to have a 100% catch rate, there’s actually a 1/65536 chance that this check will fail. This gives the master ball a 99.994% success rate.
In generation V and later, this glitch was fixed
