Legendary Artifact {4}, {T}, Sacrifice Mindslaver: You control target player's next turn. (You see all cards that player could see and make all decisions for the player. He or she doesn't lose life because of mana burn.)1
You control the entire turn, from untap step to the cleanup step. This includes playing spells, abilities, declaring attackers, assigning combat damage, and so on. [Mirrodin FAQ 2003/10/01]
You can see everything that player can see but you normally could not, including that player's hand, face-down creatures, and any cards in his or her library that they are allowed to look at. [Mirrodin FAQ 2003/10/01]
You can take control of your own turn, but this has no real effect. You still lose life from mana burn. [Mirrodin FAQ 2003/10/01]
You cannot make the other player concede. [Mirrodin FAQ 2003/10/01]
If another effect occurs that takes control of the player's actions, such as Defensive Formation taking control of combat decision, then the other effect takes precedence. [Barclay 2003/10/10]
Mirrodin
(Rare)