Just level it up to Lv.20 or over! simple.
Lv20
A Magikarp can evolve into a red Gyarados. The Magikarp needs to be a shiny Magikarp in order for it to evolve into a red Gyarados. This is due to the red Gyarados simply being a shiny Gyarados.
Gyarados doesn't evolve as it is the max evolve form of magikarp. Magikarp evolves into Gyarados at level 20.
In Pokémon Ruby, Magikarp will evolve into Gyarados at Level 20.
same lvl as a normal magikarp 20 and the shiny magikarp evolves into a red gyrados
Magikarp evolves at level 20.
You evolve it at level 20
Lv20
magikarp evolves at level 20 in all games
Gyarados does not evolve any further, it is the final evolution of Magikarp.
Magikarp will evolve into Gyarados.
It's shiny! I hope you caught that... it will evolve into a red Gyarados.
Magikarp evolve at level 20.
Magikarp evolve at level 20.
Magikarp can evolve into Gyarados, starting at level 20.
A Magikarp can evolve into a red Gyarados. The Magikarp needs to be a shiny Magikarp in order for it to evolve into a red Gyarados. This is due to the red Gyarados simply being a shiny Gyarados.
Get the Exp. Share and let your Magikarp hold it. When you battle, use a strong Pokemon and Magikarp will get some Exp. That's how I got my Magikarp to Evolve.