You evolve Inkay by hold your 3DS upside-down when it levels up to level 30, and mine is at level 29. Just wondering, will Inkay evolve if you hold your 3DS upside-down while feeding it a Rare Candy?
Yes, it will evolve. You need to hold the 3ds upside down to make it evolve while it levels up, so yes, it will evolve :D
Source-Experience + I tried it out myself :D
I'm quite sure it will, since leveling other Pokemon with rare candies to their evolution level will make them evolve.