Jaathik, of Greater Knowledge

Your opponents play with their hands, face-down permanents and cards in exile, and non-library hidden zones revealed.
{u}: The next spell you cast costs {2} less to cast. Activate this ability no more than once each turn.
{7}{b}: If {7}{b} was spent to activate this ability, you control target player during that player's next turn if that player controlled his or her last turn.