So much ideas popping out of my head. Also you could see her hair are mixed with orchid and blue because I don't have the right colored pencils for the pictures, especially the ponies.
I was thinking about Rarity being Vega because Vega is my favorite character of Street Fighter, so here's Rarity dressing up on her another dress for the Gala.
Rarity is from Hasbro
Pose based on Vega/Balrog of Street Fighter