It was pretty late at night. I had just gotten my hands on a program that gave me the ability to customize your Pokemon's sprite in-game. I was ecstatic to be able to put a sprite of my own modification into an actual Pokemon game. So I got to it, adding a top hat to my favourite Pokemon, Slowpoke. After a few minutes, my dapper pocket monster was complete. I used a GameShark code to edit the values of the game, so that a Slowpoke would be the next Pokemon I encountered, carried the edited data over, booted up FireRed, and was ready to catch myself a fancy new friend.
That's when weird stuff started to happen. The next Pokemon I encountered was indeed a Slowpoke, but something was seriously wrong. It's eyes were pure black, it's body was white, and it's muzzle was the colour of dried blood, with a fresh red colour atop it's muzzle and coming from it's bottom lip. This freaked me out pretty bad. But that's when I noticed that the Pokemon I was battling wasn't a Slowpoke at all. It's moveset was similar to that of a Pidgey, which made sense considering this was just outside of Pallet Town. When I captured it, the Pokemon slot where it should have been was more or less empty, except for this black pixelated haze and a disturbing cry I didn't recognize. Freaked out, I shut the game off, and decided to remove all my cheats and mods. After that was done, I booted the game again.
Everything proceeded as normal from there. My Bulbasaur had evolved, I had caught and evolved two Caterpie into Butterfree, as well as having a Pidgeotto. Feeling confident enough to take on the first gym leader, I saved and shut down, figuring I'd take a speedy shower before proceeding.
I came back and got my game running. But I noticed my game's save file was different. The spot where I normally had my name was instead a strange number pattern. I did a little looking around later and now know that the number pattern was actually the first part of the GameShark code for inserting Slowpoke into the wild. Kind of freaked out, I clicked the strange save file and went to the gym. I skipped past the extra guys and went straight for Brock. The battle started with him sending out his Geodude, followed by me throwing down my Pokemon. I was expecting Ivysaur to pop out, but instead what I got was the same creepy, distorted Slowpoke, this time as a back sprite. It's name still read Slowpoke, but it's gender and level were the same as the first one I had encountered. It had all of my Ivysaur's moves, with the exception of Transform replacing Leech Seed. I figured I would try it out. But what happened was my Slowpoke turned into an Ivysaur sprite, with the name and level unchanged. This time, the area that should have been Leech Seed was a strangely distorted action panel with no PP or element on it, saying only "Run". I couldn't help but be curious, so I clicked on it. My screen then started to freak out, flashing between different colours. I got scared and turned the game off. I completely stopped using GameShark codes and modding programs, and every now and then my animations will be glitchy, or a Pokemon in any area of the game will show up as Lvl 4 and female. This actually happened to Zapdos when I got there. Upon attempting to catch it, however, it simply said "Got away safely!" And the Zapdos was gone.
After that evidence of something being wrong still popped up, I put a stop to my playing FireRed, and haven't touched the game since.