Magikarp

Magikarp (Japanese: コイキング Koikingu) is a -type Pokémon introduced in Generation I. The only moves that can be learned by Magikarp are Splash, Flail, and Tackle, but the move Bounce can also be learned via breeding. (It can also learn Bounce through move tutor in Gen 5.)

Physiology
Magikarp is a Fish Pokémon. Its body is made up of red scales. Its fins are either yellow or white. They also have "whiskers" or Maxilliary Barbells. Female Magikarp have white barbells while male Magikarp have yellow barbells. Magikarp refers to them as his magnificent barbs in PokéPark Wii: Pikachu's Adventure. The way to tell a male and female Margikarp apart is that a male Magikarp has gold whiskers whilest a female has white whiskers.

Special abilities
Magikarp have the ability Swift Swim, which increases Magikarp's Speed when it is raining. Despite being strong in the past, its descendants are considerably weaker. It struggles to swim against even the weakest of currents.

Evolution
Magikarp evolves into Gyarados at level 20.

Game info
Magikarp is the most common Pokémon in the waters of all the Pokémon regions. It can be found in every body of water in Kanto, Johto, Hoenn, and Sinnoh. It is considered to be the weakest Pokémon because it can only use three moves. It is a hardy Pokémon that can thrive in any body of water, no matter if the water is freshwater or saltwater. It can even thrive in polluted waters. However, if it is taken care of properly, it evolves into a magnificent Gyarados, at level 20. Until it reaches level 20, it is pretty much useless.

In the anime
Magikarp first appeared in the anime in Episode 001 - "I Choose You, Pokemon!" When Ash and Pikachu are fleeing from a flock of Spearow, they jump into a lake to escape, and a Magikarp is seen swimming away followed by a Gyarados, which chases Ash and Pikachu out of the lake.

Magikarp's first major appearance was with Team Rocket in Episode 015 - "Battle Aboard the St. Anne". James gets a Magikarp from a dealer, who cheated his money or bottle caps three times in the whole series of Pokémon Anime, in a golden Poké Ball, of which the gold color disguised the red part of the Poké Ball. It then evolves into a Gyarados, when James kicks it away after the ship sank. The newly evolved Gyarados then uses Dragon Rage to send Ash, Misty, Brock, Pikachu, and Team Rocket blasting away to an island.

Trivia

 * Magikarp are commonly known as the weakest Pokémon in the games. Based on Base Stat average however, Sunkern would be the weakest.
 * Magikarp isn't even in the list of the Top 10 Pokémon With the Weakest Stats.
 * It is one of few -Pokémon that cannot learn Surf.
 * This is the only Pokémon that an Old Rod can catch in R/B.
 * In Pokemon Platinum Magikarp is the lowest, and also the highest level non-glitch Pokémon available for capture at level 1 and 100, beating out even the level 80 Arceus for highest. It is only available in a pond in the Resort Area with a Super Rod in Platinum, where only Magikarp can be caught and range in level anywhere from level 1 to 100
 * Its Japanese name is Koiking, which means "King of Koi." However, Magikarp is one of the weakest Pokémon.
 * Pokémon Mystery Dungeon: Explorers of Darkness, Time, and Sky are the only games where Magikarp can be taught a TM move, such as Wide Slash.
 * Magikarp is one of the only Pokémon that doesn't learn moves better than its evolution.
 * Even if a low-level Pokemon were to beat a very high level Magikarp, they would barely get any Exp. Points from defeating it, showing how bad Magikarp's stats really are.
 * Magikarp is one of 18 Pokemon that cannot learn any TMs.
 * Magikarp is inspired by the Chinese story of a carp swimming up a river to transform into a mighty dragon.