Magikarp is available in the following games:
- Red/Blue/Yellow/FireRed/LeafGreen (any body of water with Old Rod; buy from Magikarp salesman in Mt. Moon Pokécenter for 500P)
- Gold/Silver/Crystal/HeartGold/SoulSilver (any body of water with Old Rod)
- Ruby/Sapphire/Emerald (any body of water with Old Rod)
- Diamond/Pearl/Platinum (any body of water with Old Rod)
- X/Y (Fish on Routes 3 and 22 and Parfum Palace; trade Gyarados in a hotel)
- Sun/Moon/Ultra Sun/Ultra Moon (Most bodies of water while fishing)
Don't mess with this fish, or you'll REALLY regret it when it evolves.
The general summary for the Magikarp line is "Grind to 20, then smash everything without Electric (or, in later generations, Rock) moves". Its widespread availability (as the only Pokemon you can catch with the Old Rod in certain games) make it also very handy if you've had bad luck with catches or are in need of a Water-type.
Alas, in Gens 2-3, Gyarados takes a nasty hit with the separation of Sp. Atk and Sp. Def, leaving its STAB on its inferior attack stat and greatly reducing its ability to run a Special Attacker set. However, it finally recovers in Gen 4 with the introduction of the Physical/Special split, allowing it to at last STAB off its monstrous Attack.
Highly recommended for any Nuzlocke... if you can stand the grind to 20.
Completed analyses of the Magikarp line so far: