What determines what will cause a sequence break?

Question

On my Leafgreen game I accidentally skipped the Poison Gym for almost the whole pre-ending. I freaked, thought it would cause a sequence break(you know, where the game glitches and you have to delete your data, because you can't move forward story-wise?). Thankfully, nothing happened other than the Gym being easier than it would've been.

On the contrary, my Emerald game did get sequence-broken, unfortunately. I decided to LV up I bit before I tackled the Flying Gym, so I went to Lilycove City. My Rival challenged me to battle, and having him challenge me before I got the Gym Badge made it sequence break. (Darn Rivals.)
So why did the sequence break happen there, but not in Leafgreen? Is it because Team Aqua was in the city? Did it not have to do with my rival at all? Again, what determines the cause of a sequence break?

Comments

i had this happen in my Black 2, but i didn't skip anything, and i had all badges

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i never knew this could happen

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What exactly happened in the sequence break? What happens if you try going to Mt. Pyre and defeating all the Aqua grunts there? When I played Emerald, I went to Lilycove City to defeat the rival and nothing bad happened to my game.

Answer 1

I highly doubt that fighting the rival caused a sequence break, especially because neither the gym battle nor the rival battle in Lilycove are part of the sequence. This is the sequence (or at least the part you're asking about).

defeat Norman
defeat Shelly at the Weather Institute on Route 119
defeat the rival at Route 119
defeat or catch the Kecleon in front of Steven on Route 120
watch Team Aqua leave Route 121
defeat some Aqua grunts at Mt. Pyre
go to Jagged Pass and watch Magma Hideout's entrance open
defeat Maxie in the Magma Hideout and watch Groudon escape
watch Team Aqua steal the submarine in Slateport City
defeat Matt in the Aqua Hideout at Lilycove City
defeat Tate and Liza

In fact, you can get all the way through Victory Road without defeating Winona, and you can go anywhere except the Department Store if you don't defeat the rival at Lilycove City
source

Answer 2

I skipped in my firered leaders a few times and didn't get glitched, so I wouldn't worry. Your emerald should work the same. It may be glitched, my sapphire glitches on occasion because it's old and overused. I suspect the same goes with you, old and beat-up emerald and fairly new leafgreen.

To answer your question fully, depending on which gym you skip has the potential to glitch. Also it could be the game cartridge itself being messed up. I skipped many gym leaders in the past and didn't get messed up. See if it happens again, if so, then your game is messed up. Otherwise it is a one-time glitch.

Comments

A sequence break isn't a glitch. It's quite common, actually.

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Then you shouldn't be worrying. I didn't really say a sequence break is a type of glitch, but I'm saying that your emerald may be seeing the end of its life and is showing it by glitching. Like I recommended, see if the glitch happens again. I assume game freak has gave some thought to sequence breaks since Pokemon is more or less a open world game.