im not sureif i understand your question, but ill try to answer it. magikarp does not evolve by an item but does evolve at lv20. hes hard to train ot because he has no attack, no that's what the exp share is for. but he is hard to train just because he need ALOT of exp to level up.
20
Level 20.
By leveling it up to a certain level
Level 20
Lv. 20
Lvl 20.
raise it to lv 20 and it will become powerful!
Magikarp evolves into a Gyarados at level 20.
It should, unless you accidentally pressed "B"
Magikarp don,t evovle with a stone it evovle at lvl 31 i think i.
If you are going to evolve a Magickarp in Pokemon Platinum you need to: 1. Go and find yourself a MagicKarp(of course if your going to evolve a MagicKarp) 2.level up that MagicKarp to lvl 20 and then it evolves.( It will learn how to use bite when it evolves). P.S I hoped this helped you!
im not sure but i think its either 13 or 20..... Magikarp evolves at level 20