Princess Luna has a blue-violet coat, aquamarine eyes, and baby blue mane. Her cutie mark is a half-crescent moon.
As Nightmare Moon, Luna acted in the manner of a stereotypical villain: Sneering, arrogant, prone to monologues, and overly confident in her own power to the point that she believes none can defeat her. She is cruel, and willing to hurt other ponies and creatures in order to secure her goal of eternal night.
During her return during Nightmare Night, it is shown that Luna's attitude towards her subjects is one filled with antiquated tradition: speaking in the "royal Canterlot voice", which means magically projecting her voice to unnecessary volumes, speaking of herself in the third person, and punctuating her words with weather phenomena, ie. lightning strikes and gatherings of ominous clouds. She also speaks in an antiquated mode of speech, using outdated words such as "thou", and "thy". Having been driven to consuming evil a thousand years ago by bitterness, Luna is dangerously sensitive to disappointment, and was shown to be prone to pessimism whenever things began going the wrong way. Although lacking malevolence in her actions, the combination of defunct traditional habits and disauger caused her to often react to the fear around her with frightening displays of magical power. When the entirety of Ponyville ran in a panic at Luna bringing several cuddly toy spiders to life, Luna eventually resorted to Bellowing "be... STILL!" accompanied by a lightning strike, and then announcing a permanent end to Nightmare Night because the citizens "chose to fear their Princess rather than love her".
Princess Luna first appeared as Nightmare Moon in Friendship is Magic, Part 1 and later in Friendship is Magic, Part 2, where she was transformed back to her original self. Luna made another appearance in Season 2's Luna Eclipsed. She is mentioned in The Return of Harmony by her sister when describing the first defeat of Discord. She then later made cameos in A Canterlot Wedding, Part 1 and A Canterlot Wedding, Part 2. Luna also appears in Magical Mystery Cure at Twilight's coronation.Luna appears in My Little Pony: Equestria Girls as her normal self and, as her human form, Vice-Principal Luna. Luna makes brief appearances in Princess Twilight Sparkle, Part 1&2.
As Luna is a Alicorn, she possess the magical powers of a Unicorn, the affinity with air and ability to interact with clouds like Pegasus, and the natural affinity with the ground that earth ponies possess. (All according to Lauren Faust)
As Princess of the Night, it is her duty to raise the moon and stars at the beginning of each night, and to lower them again upon morning. In modern day Equestria, and she and her sister manipulate the sun, moon, and stars, though it is shown in Hearth's Warming Eve that prior to Equestria's founding, the unicorn tribe performed this duty, implying all unicorns are able to perform this magic.
Both Luna and Nightmare Moon demonstrate weather manipulation, though unlike Pegasus ponies she can command this with her unicorn magic. One of the more frequent uses of weather magic is lightning strikes, using it to defeat the Royal Guard in Friendship is Magic, Part 1 and often both as Nightmare Moon and Princess Luna to punctuate her speech. She is powerful enough to move large quantities of cloud at once and produce multiple simultaneous lightning strikes.
She has been shown to be capable of speaking extremely loudly, adding a reverberation effect to her voice which allows it to travel some distance. Luna states that this voice is the "Royal Canterlot Voice" and that it is tradition to address her subjects using that much volume. She can use a softer voice, as shown when speaking upon Nightmare Moon's return, but expressed doubt that she could learn to break the habit of it when speaking to her subjects.
She also demonstrates shape-shifting ability, shifting into a starry haze and the Shadow Bolts in Friendship is Magic Part 2 and into Nightmare Moon in Luna Eclipsed (although she did have to wear fake fangs).
As her older sister, Celestia, and unicorns like Twilight Sparkle can teleport, it can be assumed that she can as well. As Nightmare Moon, she travels as a starry haze to follow the Mane six on their quest to find the Elements of Harmony. As with her sister, she seems to prefer to travel by walking, flight, or carriage usually.
As a winged unicorn, she is very old despite her young appearance, and like her older sister possesses vast and mostly unseen magical powers. Other minor abilities she's shown to perform are telekinesis, magically enforced physical force, bringing inanimate objects to life,
- Luna was intended to reappear in Season One, to illustrate that darkness doesn't have to be evil. However, nameless people attached to the production did not feel this was appropriate, and thus she was benched.
- She appears in Season Two, the moral of the story as dictated by Twilight Sparkle, that just because someone appears scary, doesn't mean that they are bad.
- As shown in episodes such as Luna Eclipsed and A Canterlot Wedding, at night, Luna has a blue mane and tail with stars in them that flows similar to Celestia's, but during the day, she has a light blue mane and tail that are much shorter, and seem like regular hair, rather than the magical starry hair.
- Nightmare Moon makes a cameo appearance in Friendship is Magic, Part 1 inside Twilight Sparkle's hourglass when the unicorn head Twilight owned passed through it as Twilight was writing a letter to Celestia warning of Nightmare Moon.
Before Luna Eclipsed, Luna easily won the quite heavily contested award for character with the most unbalanced ratio of screen time to fan work featuring her. This is not entirely odd, the screen time she got as Nightmare Moon, along with her substantial back story and appearance early in the series made her attractive to fans, and indeed the lack of insight into her personality meant she was a blank slate for them to work with.Though many different interpretations emerged, the dominant was characterized by a shy, morose, childlike personality, with plentiful goth overtones. Some of the most influential were the works of Egophiliac, who’s extremely popular works substantially explored the relationship between Luna and Celestia.
Another common element in Luna's fandom personalities is her thousand-year culture shock. Most fans will often portray her as being behind-the-times (none memorable fan fiction, she even preferred to use an abacus as opposed to a calculator, which has since stuck with much of the fandom in a way reminiscent of Derpy Hooves' occupation of being the mail mare), and thus will have her spend most of the story trying to have her catch up to the here-and-now.
The clamor for her return remained strong, despite or because of her name not even being mentioned through the rest of the first series. The mention of her name in The Return of Harmony pleased some, but others questioned why there was still no explanation of where exactly she had been since her redemption.
Due to this weight of expectation, the fandom was united in excitement and apprehension when it was announced she was finally to get an episode. Many people predicted the fandom would explode, unable to cope if Luna was even slightly different from her fan persona. This was compounded by the amount of expectation, people had spent an entire season waiting for her return and there was no way the final reveal could possibly do anything but disappoint.
And then the episode aired. Pretty much everyone loved it, and the canon Luna. A meme started up, “Canon Luna is the best Luna”. Some people even named it their favorite episode so far.