Yugaxx, Reality Breaker

At the beginning of your upkeep, choose target opponent. Until end of turn, that player can't
cast spells, or activate abilities and you may look
at their hand and the top card of their library
any time.
You may play lands and cast spells from that
player's hand or the top card of their library
any time, and you may spend mana as though
it were mana of any color to cast spells this way.