Nightmare Moon (梦魇之月)

She was the corrupted form of Princess Luna, the younger sister of Princess Celestia who was consumed by her own jealousy toward her older sister. As Nightmare Moon, she acted as Celestia's archenemy until she was restored to her normal form by the Mane Six.

Spell casting,
Flight
Immortality, Magic,
Moon Control, Shapeshifting,
Telekinesis,
Cunning intelligence,
Umbrakinesis, Chronokinesis, Orinokinesis, Lunakinesis

Tormenting ponies' dreams

Malefic,
Abuse of power,
Invading dreams, Treason,
Attempted sororicide,
Attempted regicide,
Attempted murder,
Assault,
Attempted sabotage,
Stalking, Property damage,
Animal cruelty,
Attempted world domination,
Attempted omnicide

Co-ruler of Equestria (formerly),
Princess of the Night

Nightmare Moon is a tall pony, the same size as Celestia and shared many similarities towards her as well. Her fur color is pitch black, and her mane and tail flow in a starry midnight complexation. Nightmare Moon wears light blue armor with a moon emblem on her chest, and a helmet on her head. Her eyes are more reptilian-like, with her irises slit.

She is shown to be very forceful and angered towards her sister, as she is the manifestation of Luna's own doubt and jealousy towards her. In an alternate timeline however, while she had shown a sort of force in her subject, she still has shown some bit of regret for her sister, and willing to listen to her subjects if they do indeed have something important to say. It's possible that Sombra's involvement made her more open-minded than she would normally be.

Princess Luna had jealousy over her sister Princess Celestia. She decides to become Nightmare Moon to be more powerful.

She is a Alicorn!