When Zhonya's Hourglass is played from hidden, can it affect units dying on other battlefields, and if multiple units die simultaneously, who chooses which unit is recalled?

Ruling: Yes, Zhonya's Hourglass can affect units dying on other battlefields when played from hidden. When gear is played from hidden, it is immediately recalled to base as a corrective action since gear cannot exist on a battlefield. When multiple friendly units die simultaneously (whether from combat damage or spells like Singularity), the owner of Zhonya's Hourglass chooses which unit to save.

Sequence:

• Zhonya's Hourglass is played from hidden
• Gear is immediately recalled to base (gear cannot exist on a battlefield)
• When friendly units die, Zhonya's ability triggers regardless of which battlefield they're on
• If multiple units die simultaneously, the Hourglass owner chooses which one to recall

Nuances:

• Zhonya's ability doesn't target units
• Combat damage is dealt to all units simultaneously, not sequentially
• If a unit dies from a spell during a showdown and another dies from combat damage, they die at different times (spell first), so the first death triggers Zhonya's