How to Make Money on Pokemon: Blue, Red and Yellow

Make sure that you have an item of reasonable value e.g. Nugget or Ultra Ball.

You will also need a Pokémon that knows Surf and Fly

Place the item on slot 6 on your items menu.

OK, talk to the man in Veridian City that teaches you how to catch Pokémon.

Next get your flying Pokémon to fly you to Cinnibar Island.

Surf up and down the right hand side of the island *east*, making sure that you keep half on the land and half off.

You will be challenged by a Pokémon with a glitched image and sometimes the name Missingno.

Defeat it and then get onto the island.  The item in the 6th slot will have an unusual symbol.  Even if the symbol shows a number, you have 99 no matter what.

Go and sell these items in a shop.  This also works with Rare Candy’s if you want to get a really fast level up.

You can also go through the Pokémon league many times.  It is even easier after the rare candy cloning.