Anyone looking to get one, this is worth the read! https://www.vg247.com/2017/04/27/pokemon-go-how-to-get-a-shiny-red-gyarados/ It does share a bit on it but if you are one of those people who prefer TLDR statements: You have to catch a lot of magikarps. Yeah, I know... Sucks but I think it is still worth it.
