When multiple units die simultaneously in combat, which unit does Zhonya's Hourglass save, and what happens if you have multiple Zhonya's?

Ruling: When multiple units die simultaneously, the Zhonya's Hourglass controller chooses which unit to save. Zhonya's must already be face-up at that moment. If you have multiple Zhonya's, you still lose one Zhonya per death prevented.

Nuances:

• All units marked with lethal damage die simultaneously during the resolution step after damage is assigned
• Zhonya's is a mandatory effect that applies immediately without using the chain
• You cannot choose not to activate Zhonya's if a unit would die