https://www.google.com/search?q=where+is+magikarp+in+pokemon+reborn&rlz=1CATQWC_enUS859&oq=where+is+magikarp+in+pokemon+reborn&aqs=chrome..69i57j33i22i29i30.6991j0j7&sourceid=chrome&ie=UTF-8&safe=active&ssui=on
i say just keep up with ground types and rock types, because water types are hard to come by. My gyardos was actually traded to me so....
Personaly, I don´t really care to form strategies or play with field effects. I just train HARD. So, in my opinion, the best thing to do is scream ¨FUCK LEVEL CAPS¨, train a bunch, screw El´s Ditto/Arceus, and move on with your day.
that should help you out. I dont even think you NEED to eveolve it because I used a Rhyhorn against Charlotte. SImple breeze, but probably becaus eif you look at my reborn team, its pretty simple to understand why charlotte was so easy