Question: what is the difference between black kyurem and white kyurem?
Answer: Its neck is the same shape, but becomes upright; White Kyurem uses Reshiram's fur and Black Kyurem uses Zekrom's skin. In both forms, the ice covering one of Kyurem's jaws (upper for White Kyurem, lower for Black Kyurem) has partially disappeared, allowing it to move its mouth.