Red — Blue — Yellow

MISSINGNO

Almost everyone has seen this glitch somewhere in their RB game. Unknown by most, MissingNO or M'Block, can be found on the strip of water one step away from the shoreline on Cinnabar Island, where most people see it, or that same area on Seafoam Island. You find them, as well as Pok�mon over level 100, after watching the old man capture Weedle.
Explanation: Gamefreak had forgotten 2 HEX values while programming. When the old man catches the Weedle, the game needs to store the trainer data somewhere. Gamefreak stored it in one of the Pokemon slots. Gamefreak's idea would have worked, had they not had forgotten to define the Pokemon in those two areas. So, you find certain Pokemon there depending on your name, not ID number. If you use a default name, though, the game randomly chooses a number.

Mew

The Mew trick, while there are many false rumours, actually does exist.

First, go through the tunnel between Celadon City and Lavender Town. Do not continue walking. Save the game.

Move forward one square and press start. You SHOULD have the menu open and the Gambler should not have noticed you tet. Use FLY to Cerulean City and fight the Youngster with a Slowpoke. Beat him.

Now FLY to Lavender Town and head towards the Gambler. The menu should pop up, so close it. You will then encounter a wild level 7 Mew. Figure out what comes next, why don't you?

Explanation: In Red/Blue/Yellow, Gamefreak forgot 2 hexidecimal numbers. Sound familiar? One was for the SP.ATK of certain trainer's Pok�mon. Also, when you fly away from the gambler, the game thinks you're battling him, so when you battle the youngster, the game thinks the gambler is the youngster. This is what kicks in the second Hex number, and since there is a opening for SP.ATK, think that the Slowpoke's SP.ATK is a pokemon. Because that Slowpoke's SP.ATK was 21, it thought the pokemon was the Pok�mon with the hexidecimal number of 15, or 21. So when you enter the route the gambler was on, the second hex number STILL thinks you're battling him, since you didn't attack any of his pokemon, so it uses the pokemon that was Slowpoke's SP.ATK, Mew.

Ruby — Sapphire — Emerald

And the Lady Jumped Over the Ledge

If you get Aroma Lady Rose, just east of Mauville, to spot you, while you are over the ledge, she'll defy gravity and walk over to challenge you. Not particularly interesting, but it's a glitch, at least.

Cloning Glitch(Emerald)

Save in front of the PC in the Battle Tower.
Deposit the pokemon you want to clone into the first slot of an empty box.
Leave the PC and save again.
Go to the PC one more time and withdraw the pokemon you want to clone, the one that's in the empty box.
Talk to the lady on the far right, and she will ask you to join a Multi Battle.
Select Yes and choose any two pokemon.
When she asks if you want to save, select Yes.
If everything so far has been done correctly, the game will wait about one second before doing anything else.
It doesn't matter what you do from here, the One Second wait was the glitch taking place.
Turn off your game, and now the cloned pokemon is both in the PC and in your party.

Randomosity requires stylesheet support. If you find any errors, contact surskitty.

Disclaimer

Randomosity makes no claims to be spoiler free.

This site is in no way affiliated with Nintendo, SquareENIX, or anything else. Pokémon is © to Nintendo, GAME FREAK and Creatures Inc. Final Fantasy is © to SquareENIX. Neopets is © to Neopets.

You are using CCBot/1.0 (+http://www.commoncrawl.org/bot.html).