Twilight Sky is a male backgroundpony with a medium gray coat, light blue mane and tail, blue eyes, and a cutie mark of three white stars. He is an Earth pony both in few in-show appearances and in all merchandise, while he is a Pegasus in most in-show appearances. He is unnamed in the show, but he is named in merchandise.
In Hearth's Warming Eve, Twilight Sky takes part in the pageant as one of the hungry Pegasus ponies living in the Pegasi's cloud city. He appears again as a Pegasus in Hurricane Fluttershy as one of the Pegasi enlisted to help with transporting water to Cloudsdale.
Twilight Sky's name comes both from the fourth and sixth waves of mystery packs, which state that he "loves to play guessing games with friends!", and from the Canterlot Nights expansion set of Enterplay's collectible card game, his card #82 R of which lists the quote "You aren't on the list? Back of the line!" and card #112 U of which, Not On the List, attributes to him the quote "Invitation only means invitation only!"
A WeLoveFine.com T-shirt titled "Rarity Prefers Diamonds" shows him, "Sir Pony Moore", Perfect Pace, and "Star Gazer" wearing jackets and bow ties.