It's the first time something like this happened to me, so I thought I'd share. I was playing the game on GameCube via Game Boy Player (using Game Boy Interface), the game was running from Everdrive-GBA X5 using LeafGreen Rev.1 English ROM.
I was going through Victory Road like normal, then Repel ran out. I wanted to apply another one, but I couldn't scroll up/down through my bag, although I could change the bag pockets. When I returned to the overworld, my player sprite and one of the boulders were invisible, and the rest of the sprites became garbage. Sometimes the screen was riddled with green vertical lines. The game finally crashed when I viewed one of my Pokemon's data.
Here's the video of the glitch. Excuse the slightly vulgar voice commentary.
Thankfully, I saved the game when the glitch was in progress. After loading the game most of the glitchyness is gone, but the player sprite and one of the boulders are still invisible. When you try to move said boulder, some weird stuff can happen to other sprites in the area (see screenshots). The game doesn't seem to crash anymore, the vertical lines are gone, and items in bag can be chosen normally. Going to another floor seems to fix this glitch entirely, I was able to beat the rest of the game without issues.
There were no cheats used, although admittedly two of my Pokemon were artificially created in PKHeX. With that said, they were normally traded from another GBA that I have using a link cable - the LeafGreen save was never edited.
I have attached the save file, just in case anyone wants to mess around with it. Any idea what has happened? Did anyone else come across such weird glitch? I'm asking just out of pure curiousity.