Pokemon R/B/Y - Hyper Beam + Sleep glitch
If a Pokemon that has just used Hyper Beam and has yet to recharge is targeted with a sleep inducing move, any other status it may already have will be ignored (paralysis/burn/freeze/poison) and sleep will be induced regardless. In addition, the sleep inducing move will NEVER miss (not even from a "255").
Normally a detailed explanation would follow but there's no need for one now because this is just a generic programming bug. Whenever a sleep inducing move is used, the "recharge from Hyperbeam" status is removed from the target, and the programmers messed up from there, skipping key parts of code of the Sleep Effect routine if that status is active.
I don't think it's possible to trigger this glitch with a frozen Pokemon since it won't be able to use Hyper Beam if frozen, so ultimately this glitch would only apply to paralysis, poison and burn.
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