I just recently acquired OPI Merry Midnight from the 2009 Holiday Wishes collection and already had Orly's Fowl Play from the 2011 Birds of a Feather collection in my stash and found out that they are practically dupes. I read it on a blog and when I first swatched them on a nail wheel they were not even close to being dupes but when I actually tried them out on my nails they I saw what the other blogger was seeing. They are so close that its hard to tell the difference.
Pinky and middle are Fowl Play and index and ring are Merry Midnight. Fowl Play may be just a shade darker if you look close. These photos were taken outdoors in natural sunlight.
So if you have Fowl Play then you really don't need Merry Midnight unless you happen upon it and want it because its considered hard to find now.
I learned not to go by how they look swatched on a nail wheel and to try it out on my nails to be sure.