Rules · PlanesAdvisor

723.5 While controlling another player, a player makes all choices and decisions the controlled player is allowed to make or is told to make by the rules or by any objects. This includes choices and decisions about what to play, and choices and decisions called for by spells and abilities. Example: The controller of another player decides which spells that player casts and what those spells target, and makes any required decisions when those spells resolve. Example: The controller of another player decides which of that player’s creatures attack, which player or planeswalker each one attacks, and how those attacking creatures assign their combat damage.

723.5a The controller of another player can use only that player’s resources (cards, mana, and so on) to pay costs for that player. Example: If the controller of a player decides that the controlled player will cast a spell with an additional cost of discarding cards, the cards are discarded from the controlled player’s hand.
723.5b The controller of another player can’t make choices or decisions for that player that aren’t called for by the rules or by any objects. The controller also can’t make any choices or decisions for the player that would be called for by the tournament rules. Example: The player who’s being controlled still decides if they will leave to visit the restroom, trade a card to someone else, agree to an intentional draw, or call a judge about an error or infraction.