When multiple units die simultaneously with Zhonya's Hourglass on board, who chooses which unit to save, and in what order are the replacement effects applied?

Ruling: When multiple units die simultaneously with Zhonya's Hourglass on board, the owner of each unit being acted on determines the order of replacement effects for their units. When units with different owners die simultaneously, turn order is used to organize the sequence.

Sequence:

• If multiple units with the same owner die, that owner chooses the order of Zhonya's replacement effects
• If units with different owners die simultaneously, use turn order to determine the sequence
• The ordering is based on the owner of the unit (not the controller)

Nuances:

• If you take control of opponent's units via Possession and they die with Zhonya's on board, the opponent (as owner) still makes the choice
• There is discussion that this should probably be based on controller rather than owner, but the current rule specifies owner