Loki: Unheard of (re: Shiny Eevee)! I have not seen a naturally occuring, or, frankly, even a Masuda-method bred shiny pokemon since catching one Way Back When while playing the original Pokemon Silver on the GBColor (I am OLD)! Awesometown.
As an aside, I looked further into the RNG manipulation for fishing pokemon last night, and it's Way less complex than I at first thought (I was just not using the right pull down menu!). I'm going to give a stab tonight at creating an RNG'd, quasi-perfect poliwag with hidden power grass [as well as the egg move Encore], and it if works - we should talk!