Grind it to lv100, give it a focus sash, and teach it flail. Make them regret taking on a shiny Magikarp.
I swear I am the master at chain fishing.
I can generally get a 70 + chain no problem, and usually find a shiny around 50 or under.
 
I GOT A SHINY MAGIKARP ON A 5 CHAIN.
IT ONLY TOOK ME LIKE 5 MINUTES.
YEEEEEEEEES ily chain fishing.
Lucky fuck! I've been chain fishing since for an hour at a time since yesterday for a Magikarp and didn't get shit! Anyway nice!
 
Got a shiny Magikarp on a 5 chain.
Got a shiny Tentacool on about 15 - 20 chain.
Got a shiny Feebas on a 50 - 60 chain.
Got a shiny Sharpedo on a 4 chain. (Literally took 2 minutes.)

GG, today is a good day.
 
Got a shiny Magikarp on a 5 chain.
Got a shiny Tentacool on about 15 - 20 chain.
Got a shiny Feebas on a 50 - 60 chain.
Got a shiny Sharpedo on a 4 chain. (Literally took 2 minutes.)

GG, today is a good day.
You flipped your shit when you got that Feebas.
 
@Sargent¥
Forgot to mention that as of right now I am undefeated by the 3 other people I have challenged, so prepare your pokemon beforehand please.

Should reiterate that one of those people was Waffles on showdown, and he beat me 2/5 times in the OU tier.
 
After playing every Pokemon since Blue/Red, I have yet to find a shiny, except the one that was given to me by Gamestop 2 years ago