Easily my shiny Clefairy on my Diamond version. I was hunting Mesprit (or was it Cresselia?). I was passing through Mt. Coronet, and I was like, "Oh, crap! Shiny Cleffa!" I ended up catching it with a Premier Ball. I think it was down to sheer luck that I caught it.
Pokemon Y Friend Code: 3282-3535-2249
Friend Safari: Pansage, Petilil, Gogoat
As of now, my focus is on Safaris with starters (barring Wartortle and Quilladin), but give me your Safari anyway. Chances are I'll find something interesting.