And here she is, a favorite no doubt, it's Princess Luna!
As I have said on the Celestia poster, I kept everything simple so they could share the same layout, thus keeping them consistent.
Two things to note:
First off, Luna's cutie mark is a prick of a thing to work with. Because it covers her entire rump, not just one image on both sides. This makes the vectors of the cutie mark have straight edges across three sides, and this makes the mark look like it ends too abruptly if you can see the straight edges.
Probably didn't explain that too well, but that's the reason why there seems to be two of her cutie marks. It really is just both sides making one image.
Secondly, I decided against adding the one line Luna has (I'm so sorry), as it didn't really fit the image. And happy Luna is nice, so deal with it.
Hasbro owns the ponies, not me. Obviously.