As you can see, I even have Sparkle Balls at the ready... but I was not prepared to find an actual, random, already-Shiny Rayquaza of all things
It got away D:
remind me to have Dusk Balls or something for the future
Edit: Wait, I might just be stupid. Do they have an increased Shiny rate? XD I've already found a second Shiny Rayquaza.