If a single unit dies while you have 2 Zhonya's Hourglasses in play, do both activate or only one?

Ruling: Only one Zhonya's Hourglass will apply. Both replacement effects are available, but you can only replace the same death event once.

Sequence:

• Both Zhonya's replacement effects apply to the same death event
• The owner chooses the order in which they apply
• The first Zhonya's replaces the death with a recall
• The second Zhonya's has nothing to replace since the unit is no longer dying

Nuances:

• Zhonya's is a passive replacement effect, not a trigger, so it doesn't use the Chain
• Replacement effects can intercede other effect resolutions
• The same principle applies to combinations like Guardian Angel + Zhonya's