Twilight Mist (or just Twilight) is a motherly unicorn pony. She has the magical ability to teleport by wishing ("I wish, I wish, I wish!"). She's protective of little Ember, which prompted her to join the rescue team (which includes Megan, Firefly, Bow Tie, and Applejack) to go to Midnight Castle.
According to Lauren Faust, Twilight is the inspiration for the Friendship is Magic incarnation of Twilight Sparkle. Creator Lauren Faust originally wanted her to be named just "Twilight" as well. Twilight Velvet, Twilight Sparkle's mother, resembles G1 Twilight in color.