to help explajn this a bit better, and to simplify things, get a male and female magikarp, take them to the battle instotute, and writoe down their level 50 stats. now go breed a magikarp, and reject the firat egg. save, then breed a second egg. accept this one, hatch it and take the lvl 1 magikarp to the battle institute. write down its lvl 50 stats, and compare them to the parents. 5 of them will match after taking into account natures. those are the five stats that will be passed down. now reset your game, and swap the magikarps out of the day care center, replacing them with the parents of what you are trying to breed, ensuring they have the IV spread that our test egg showex would vet passed frkm each parent. breed out the egg, and when it hatches get it chdcked. if done roght, you shojld have a 5 IV kid, with that spread.
pardon the typos. on my phone and it starts to glitch out when the posts get too long.