Princess Luna is a fan-favorite among the G4 crowd. She's a mysterious, dark pony who is, at times, endearingly awkward while learning to adjust to modern-pony times after being exiled to the moon.
She's a powerful princess pony with both a magic unicorn horn and big pegasus wings.
In the toyline, she's purple. The 2011 release is the small normal-sized pony with a glittery horn, wings, and cutie mark and tinsel in her hair.
She has a weird, unique eye shape that doesn't really look like any other pony's in the show or toyline.
She came in a two-pack with a pink Princess Celestia that has molded hair. This small Luna can go for around $30 second-hand (I didn't pay that much!).
The bigger Luna uses the alicorn mold that would be used for Princess Cadence and Twilight. She came packaged with Rarity.
There were two versions of this Luna, both having slightly differently colored heads.
Though her appearance in the toyline didn't always match how she looked in the show, toyline Luna is cute. Her glittery hair and sparkly bits are cute!
She had quite a few releases in the G4 toyline and also made it through the transition to G4.5 (also known as Pony Life).