I came across this video
while shifting through my YouTube feed, and at first glance, it's only a minor glitch; if you mash X while waiting for an unbattled trainer to turn towards you, you can open the menu just as they look at you. As the video states, you can immediately back out to battle, or save, reset, and immediately battle the trainer upon the game's startup. Flying away is also pretty boring, since it goes straight to the cutscene.
However, the video did not try to use the Eon Flute to fly away, which could theoretically be accessed by registering it as a Key Item and spamming Y instead of X. Additionally, I believe using Dig and/or Escape Rope in a cave also forces you to undergo an overworld animation. Because I already defeated every Trainer that I could potentially use for this glitch, is there someone who could test this out? I seriously doubt it would amount to anything, but it'd be interesting at least.