What is the worst glitch in Pokémon? There's a lot of trickery that you can do with Gen I (and II, to a lesser extent) that can perma-fuck your game, but usually you have to know what you're doing to perform them anyway, and if you save after it's your own damn fault.

Then there are some glitches that can break the game with no prior knowledge, like the broken escalator in Japanese D/P, the frozen Zoroark in Japanese B2W2, or the Lumiose save glitch in X/Y. But those first two are only in the Japanese versions, and the last one got patched. My thoughts are with your deleted save files that got affected by that glitch btw

But I still maintain the worst one is the berry glitch. Yes, the game can still be played, but it's unavoidable and hard to fix. And it's really annoying not being able to grow berries, play the lotto, or never being able to go to Mirage Island. But the worst part is having to skip through the "The internal battery has run dry blah blah blah" message every time you play the game.

I just really hope they don't have a save-breaking glitch in S/M. If they do I hope it gets patched quickly.