A Magikarp living for many years can leap a mountain using Splash. The move remains useless, though.
Magikarp have an easter egg: a “Roasted Magikarp” skin if they have been struck by lightning. The skin is a paler color that implies being “cooked” and has crosses for eyes. If a roasted Magikarp is evolved, the resulting Gyarados will have a special “Zombie Gyarados” skin.