Rule 711.4

The controller of another player's turn makes all choices and decisions that player is allowed to make or is told to make during that turn 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 the turn decides which spells the active player casts and what those spells target, and makes any required decisions when those spells resolve. Example: The controller of the turn decides which of the active player's creatures attack, which player or planeswalker each one attacks, what the damage assignment order of the creatures that block them is (if any of the attacking creatures are blocked by multiple creatures), and how those attacking creatures assign their combat damage.

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