I've been doing a living dex while capturing all Pokémon in their home generation, and it was going fairly well. I was lurking around on IGN/GameFAQs and someone had suggested a very interesting way of doing the long range trainer glitch. Without using Ditto or a specific special stat. It seemed fairly intriguing to me, and I was looking for a stable MissingNo. (apparently x4 harder to encounter on Yellow VC than cartridge) to get lots of rare candies.
Note: I used the debug menu on VC to make the game go x10 its normal speed. I doubt this had anything to do with the save file, however.
I'm sure it's nothing new, but here are the steps I took:
1. Fly away from the kid west of the Cerulean bridge.
2. Save my game by changing a PC BOX and restarting the game.
3. Fly away from the gambler near Lavender Town.
4. Save my game by changing a PC box and restarting a game.
5. Battle a trainer that is more than one tile away.
6. Talking to a NPC that wants to trade and selecting 'NO'
* Here's the thing with this one: The tutorial said to use the girl who asks for a Cubone south of Cerulean, but I had already traded her so I had the genius idea of going to the Pokémon lab in Cinnabar instead. More on this later.
7. Fly to Cerulean.
8. Go up to Nugget Bridge. The menu pops up, but instead of pressing B, I flew to Lavender Town as per the tutorial.
9. Fight a Level 80 Starmie as SOON as I landed outside the Pokémon center.
* This actually changed based on the trainer I spoke to. I eventually did try the girl in Cerulean. Here's my results.
Cubone for Machoke Girl: Level 80 Starmie
Golduck for Rhydon: Level 80 Starmie
Growlithe for Dewgong: Level 100+ Electrode
Kangaskahn for Muk: Level 100+ Kingler
10. Walk to Route 8.
11. Press B when the start menu comes up, triggering another battle.
There's quite a lot of RNG involved in this and that was kind of fun about it. It seemed as if each NPC had their own batch of Pokémon that was encounter-able after speaking to them because I would encounter the same few or so. Sometimes glitch trainers appeared or trainers who had the wrong roster. Several times I encountered Lance with an unglitched 152 level Squirtle or Bruno with Blaine's team.
All of the MissingNo. encounters I had seen so far had crashed my game, but I was able to trigger a battle with and actually 'fight' it because the cry was sped through. Until the game crashed, haha.
On one of my encounters after 100+ Kingler, I encountered a glitch Pokémon that crashed the game on encounter. Not the first time. Shrugged it off, reset through the debug menu, was ready to play some more RNGesus. File was gone. No indication of corruption.
Okay, cool! It seems valid on SaveDataFiler. Oh, it won't open on PKHex? Or Rhydon? This isn't good. I opened up the file in a hex editor and compared it to a 'clean' file and it seems the entirety of Bank 1 was overwritten with garbage.
First one is garbage, second one is clean. Let me reiterate, this Pokémon did not use any move whatsoever or barely even showed its sprite. The game crashed two seconds after encountering it.
I get my mistake. :P I really should have made a back up of my file using JKSV before I did this, but it didn't cross my mind that merely encountering a glitch Pokémon would erase my file. I mean, I have several cartridges and have abused them a lot glitch-wise, but outside of Super glitch or other ZZAZZy shenanigans, the Bank 1 being overwritten on encounter has NEVER happened to me. While it sucks to have to restart my dex, I think it might be a lot less hair raising to do it in Red and Blue anyways… I'm more surprised that I encountered anything like this and dealing with RNG was kind of fun. (Not sarcastic)
If this has happened to you, please tell me! I might try to recreate it on a copy VC (force a different title ID) but not risking my main file ever again with something like that.