Can a Yasuo player unhide Zhonya's Hourglass from a battlefield to return it to their base, or is it stuck at the battlefield once hidden there?

Ruling: Gear cannot exist at battlefields, so when Zhonya's Hourglass is played/unhidden from a battlefield, it immediately gets recalled to base. You can play a card from hidden any time you can use a reaction, so you don't need a friendly unit to die to unhide Zhonya's.

Sequence:

• Unhide/play Zhonya's Hourglass from the battlefield (can be done any time you can use a reaction)
• Zhonya's immediately returns to base (since gear cannot exist at battlefields)

Nuances:

• A friendly unit does not need to die for you to unhide and play Zhonya's Hourglass
• The card can be unhidden whenever you can use a reaction, not just when its effect would trigger