Can a hidden Zhonya's Hourglass in one battlefield be used to save a Carnivorous Snapvine in a different battlefield from trading with an enemy unit?

Ruling: Yes, a hidden Zhonya's Hourglass can save any unit anywhere on the board, not just units in the same battlefield. However, the Zhonya's must have been hidden on a previous turn, as hidden cards cannot be flipped on the same turn they were played hidden.

Sequence:

• Play Zhonya's Hourglass hidden in a battlefield on an earlier turn
• On a later turn, play Snapvine in a different battlefield and target an enemy unit
• Flip the hidden Zhonya's to protect the Snapvine from the trade

Nuances:

• The FAQ clarified that Zhonya's no longer has a "here" restriction when played from hidden and is treated as a global effect
• "While hidden" is different from "from hidden" - the card must be flipped/activated from hidden to get the global effect