Well... Even though I do like Magikarp, that doesn't change the fact that it isn't very good, even in LC. Magikarp only gets five moves; Splash, Tackle, Hydro Pump, Flail and Bounce.
Since Splash doesnt do anything, that should be removed.
So now your moveset will be
Magikarp could be used to finish off low-health opponents. Giving it a choice scarf and speed EVs can help you with that. Attack/Special Attack EVs can help you do some more damage too.
This is Smogon's Strategy guide for Magikarp.