The pack includes Tanooki Mario, Cat Peach and Link as new playable characters, plus four vehicles and eight courses (that's two new cups with four courses each).
A second DLC pack for Mario Kart 8 is due out in May 2015, called "Animal Crossing X Mario Kart 8." It includes new playable characters in Isabelle, Villager and Dry Bowser, plus four vehicles and eight courses. Purchase both packs in a bundle or separately and snag eight different-colored Shy Guys and eight different-colored Yoshis. Score.
Mario Kart 8 (AOC Pack 1)