Big news for fans of sugary breakfast cereals and social-media-driven brand promotions: Lucky Charms is giving people the chance to win "the unicorn of the cereal world," a box of Marshmallow Only Lucky Charms, People reports. According to General Mills, the contest is in response to the constant requests the company gets for an all-marshmallow box of the cereal. Also, Biz Markie is involved for some reason. To win one of only 10 boxes being made available, post a selfie of yourself holding an imaginary box of Lucky Charms to Facebook, Twitter, or Instagram and tag it #Lucky10Sweepstakes by Sunday. Or, you know, just buy one of these. (More cereal stories.)