Once day after I win fight a girl trainer on Lake of Rage and she talking about pink Butterfree
Finding shiny pokemon is simple always a 1/8192 chance, which a few things that are manipulated.
But for the most part, I think they basically threw that in there because the Shiny Gyarados is actually IN the Lake of Rage.
If you haven't caught it yet, sorry for the spoilers!
Yes you can but there is a 1/8192 chance . Masuda Method don't works here :-(