Evolve without a Stone in RBY
Posted by: rby4ever
Date: 2007-03-09 23:41:27
Yeah, this is an old one, but hey… might as well go for completeness… besides, many people believe some misconceptions about the glitch, and they should be cleared up.
The long and short of this glitch is that if you want to evolve a "stone evolver" (Clefairy, Staryu, Pikachu, etc.) without actually using a stone on it… you can do so by having that monster level up during a fight, then by finishing the battle (trainer, wild, it doesn't matter) with a specific Pokemon.
You see, a handful of the Pokemon out of the 151 have a HEX number corresponding to an evolution stone. Here is a list:
Moon Stone - Exeggutor
Fire Stone - MissingNo. (It has to be a HEX 20 Missingno., no other will work!)
Leaf Stone - Psyduck
Thunderstone - Growlithe
Water Stone - Onix
Doing the glitch is simple: just have the stone evolver in the first position, and have the corresponding monster from the above list somewhere else in the party (doesn't matter where). Have the stone evolver gain a level during the fight, and finish the battle with the other monster (if this is a wild battle, you'll obviously have to switch to the 2nd monster right at the beginning). If you've done everything above correctly, the stone evolver will evolve at the end of the fight.
The reason this happens is because the two operations, detecting a used a item and detecting the monster that is out, happen to share the same variable. The variable is 01XX91CF for Red and Blue, and 01XX90CF for Yellow. Use a Potion, and this variable is filled briefly by "14". Enter a battle, and send out a Pidgey, and the variable will become 24.
You might be wondering what the usefulness of this glitch is. For the most part it isn't that useful, since you can just buy most of the stones in the Celadon mall. However, Moon Stones are limited (only 5 in the game, 2 of them being hidden items), so it's quite nice to only need an Exeggutor to evolve a Clefairy or Nidorino. This trick also lets you evolve a yelllow-version Pikachu without having to trade it to another cartridge.