Well, the roster includes not only Pyramid Head, but Robbie the Rabbit from Silent Hill, making this officially the creepiest kart racer ever. In fact, the App Store description says, "If you have trouble staying on course try using Robbie the Rabbit. He's a bit slow but easiest to control." He's not just in the game, he's the beginner character!
Other confirmed characters ("confirmed" meaning we see them in screens) include Power Pro-kun, Frogger, Evil Rose from Rumble Roses ( ... ), Sparkster, Pentarou, Goemon, and Tako from Parodius.
Krazy Kart Racers (Konami, $7.99)