Magikarp is one of the most iconic Pokémon, if only because it is so weak and worthless. If you're ready to take on a challenge, you can try to get Magikarp to Level 100. However, most players will want to evolve him into his much more fearsome form, Gyarados, as soon as possible. If you're playing Pokémon X, Y, Alpha Sapphire, Omega Ruby, Sun, or Moon, you can even level up your Gyarados by using a Mega Stone.
Steps
Part 1 of 3: Evolving Magikarp

Step 1. Decide if you want to evolve it
While there isn't much to gain from raising Magikarp's level for longer than it takes to evolve it, there are certain instances where it might be a better idea to keep a Magikarp.
- A Shiny Magikarp is a very nice trophy and the Pokémon it turns into after its evolution (Shiny Gyarados) is one of the most common Shiny Pokémon in the game.
- You can try as a challenge to make Magikarp reach Level 100. A Level 100 Magikarp is also a good commodity because it is difficult to get hold of.
- When Magikarp reaches Level 30 he will learn Flail. This is a very powerful move for when your Pokémon is injured, which can make it a dangerous choice. If Flail is a good fit for your play, it may be one of Gyarados' most powerful moves and it may be worth not letting your Magikarp evolve until it learns this move.

Step 2. Magikarp must have reached at least Level 20 before you can evolve it
Once Magikarp reaches Level 20 he will try to evolve. You can prevent him from evolving by holding down 'B' during evolution, or you can have him evolve into Gyarados.
See the next section for some ways to help Magikarp reach Level 20 quickly
Part 2 of 3: Ways to train Magikarp quickly

Step 1. Have Magikarp join a battle and then immediately take him out again
You will need to do this for most battles as Magikarp has no attacks on its lower levels. As long as Magikarp participates for a round, he gets a share of the experience.

Step 2. Equip Magikarp with an Exp Share
This is an item that gives the Pokémon it owns a share of the experience gained during a battle, even though the Pokémon itself did not participate in the battle. He will still need to be part of the active group, but you won't have to worry about throwing the Pokémon into battle, and then immediately taking it out again.

Step 3. Send Magikarp to the Day Care Center
To allow Magikarp to automatically earn experience, you can leave it at the Day Care Center in the game. It will take a while as the rate at which the Day Care experience is earned is slow, but you won't have to fight or keep the Pokémon in the active group.
Your Magikarp will not evolve in the Day Care Center even if it reaches levels higher than Level 20. After you retrieve it, it will attempt to evolve immediately after its first battle if it meets the requirements for reaching that level. has

Step 4. Feed your Magikarp Rare Candies
If you have a stock of Rare Candies, you can quickly get your Magikarp to reach the level you want it to be. If you feed him a candy that makes him go from Level 19 to Level 20, he will begin to evolve.
Part 3 of 3: Evolving Gyarados into Mega Gyarados

Step 1. Get and upgrade your Mega Ring (X and Y)
To evolve Gyarados into Mega Gyarados, you must first obtain your Key Stone, which is embedded in a Mega Ring. To get the Mega Ring you will need to defeat your rival and then earn the Rumble Badge in the Shalour Gym. Bring the badge to the top of the Tower of Mastery to receive the Mega Ring.
- After getting the Mega Ring you will need to upgrade it by beating your rival again in Kiloude City. Professor Sycamore will upgrade your ring after the battle.
- Click here for more details on the Mega Evolution process in X and Y.

Step 2. Defeat Groudon or Kyogre (Alpha Sapphire and Omega Ruby)
To access the Mega Stones in Alpha Sapphire and Omega Ruby, you must first defeat the Legendary Pokémon. These are Kyogre in Alpha Sapphire and Groudon in Omega Ruby.

Step 3. Locate the Gyarado site
This is the Mega Stone needed to evolve Gyarados into its Mega Form during battle. The location of the Gyarado site depends on which version of the game you are playing. The ground will shine where the Gyaradosite is located.
- X and Y – You can find the Gyarado site in Couriway Town, close to the three waterfalls on the eastern side.
- Alpha Sapphire and Omega Ruby - Find Chomper the Poochyena along Route 123. You can find him at the 123 Go Fish store. Give Chomper a swipe to receive the Gyarado site.

Step 4. Have your Gyarados hold the Gyarado site
This is necessary for him to Mega Evolve during battle.

Step 5. Click on 'Mega Evolve' during battle to turn into Mega Gyarados
You can only have one Mega Evolution active per battle. It will keep its Mega form if you swap it with another Pokémon during battle. The Mega Evolution will remain active until the battle is over, or until the Gyarados faints.