How to Easily Get the Red Gyarados in Pokemon Ruby
The Pokemon Red Gyarados is an unusual Gyarados that is shiny, unlike the typical blue dragon-like Pokemon. It is red because it evolved so rapidly from Magikarp that it didn't have time to change colors. The chances of getting a shiny Gyarados, regardless of what game you are in, including the Game Boy Advance game "Pokemon Ruby," are one out of 8,192.
Instructions
1
Go to Sootopolis City.
2
Fish in the lake for a Gyarados.
3
Continue fishing in the lake until you get a shiny, red one. If you are persistent, you will catch one eventually.