Sorin Markov

While controlling another player, you can see all cards in the game that player can see. This includes cards in that player’s hand, face-down cards that player controls, and any cards in that player’s library the player may look at.

Controlling a player doesn’t allow you to look at that player’s sideboard. If an effect instructs that player to choose a card from outside the game, you can’t have that player choose any card.

In a Two-Headed Giant game, Sorin’s second ability causes the targeted opponent’s team’s life total to become 10. Only the targeted player is actually considered to have actually gained or lost life.