Masquerade

Masquerade is the placeholder name of a female background Earth pony with a light yellow coat, royal blue mane and tail, green eyes, and a cutie mark of a pink six-pointed star surrounded by five smaller white stars.

Design
Masquerade shares her color scheme and dress color scheme with fellow Gala guest "Gold Slipper", and her cutie mark is the same as that of Twilight Sparkle and in some depictions Photo Finish.

Depiction in the series
Masquerade is a guest at the Grand Galloping Gala in The Best Night Ever. She also appears in Sweet and Elite, in A Canterlot Wedding - Part 2, in Magical Mystery Cure, in Princess Twilight Sparkle - Part 1, in Power Ponies, in Rarity Takes Manehattan, in Simple Ways, in For Whom the Sweetie Belle Toils, in Equestria Games, and in Twilight's Kingdom - Part 1.

Appearances
Times are approximate.

Depiction in the comics
On the IDW comics' page 8 and  page 14, Masquerade appears in nightmares that Pinkie Pie has.