MrCheeze | Revealing hidden Pokemon via memory corruption - Pokemon Gold 1997 Spaceworld Demo @MrCheeze | Uploaded June 2018 | Updated October 2024, 3 days ago.
In the 1997 Spaceworld demo for Pokemon Gold and Silver, the player is restricted to a small area with only a few Pokemon available. However, in this video I demonstrate that with a modern understanding of Pokemon memory corruption glitches, it is actually possible to see almost all of the 251 Pokemon programmed into the game. No use of debug features is necessary (in fact, the method shown here doesn't work in the debug rom), so hypothetically anyone could have done this way back in 1997. It's possible Game Freak may have suspected their game was exploitable, as no photography was allowed at the original event.

The key to this strategy is that the player must obtain 8 different items in their bag. At that point, the "select glitch" can be used to swap out-of-range Pokemon with each other, so that the first character of one of your Pokemon nicknames overwrites the species value for one of your Pokemon.
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The 8 items are obtained as follows:
- Player begins with Poke Balls, Potions, Full Heals, Stimulus Orb (prevents sleep), and Focus Orb (proto-Focus Band).
- Starter Pokemon holds a Berry, which we take from it. All Pokemon obtainable in the wild also have a 25% chance of carrying a Berry, with the exception of...
- Wild Girafarig have a 25% chance of holding an Apple (proto-Gold Berry), only in the Gold non-debug build of the game. In Silver, and Both debug builds, they instead will carry a Berry. We need to catch an Apple-carrying Girafarig, without causing it to eat its item or using up all 5 of our Poke Balls.
- All of the above adds up to 7 items, so we can now swap one of our Pokemon with an out-of-range one, giving us a glitch Pokemon that happens to carry an 8th item that we can take from it.

During the above process, we made sure that the first character of the nickname of one of the Pokemon we caught matches the ID of the Pokemon we want to obtain - in this case, character "5" = F5 = Leafeon. At this point it just becomes a matter of making the right swaps to overwrite our first Pokemon's species byte with this value.

In this case, the end result happened to be a Leafeon at level 0 with no HP - but by using another select glitch, I was able to give it experience from another Pokemon's battle and bring it to a usable level. Unfortunately, virtually all the hidden Pokemon have extremely low base stats making them still very hard to use.

If anyone had actually done this at Spaceworld 1997, Leafeon would have been discovered a good 9 years before its actual release in Pokemon Diamond and Pearl in 2006.