When Zhonya's Hourglass is flipped from hidden, does it go to the battlefield first and then get recalled to base, or does it go directly to base? Can you flip it at any time and have it wait in base until a unit dies?

Ruling: You can flip Zhonya's at any time when you have priority at reaction speed. When a Gear is at a Battlefield for any reason, it is immediately recalled to its controller's Base as a corrective action.

Sequence:

• Zhonya's is flipped from hidden and goes onto the chain
• As a permanent, it immediately resolves (not reactable)
• The Gear is recalled to Base as a corrective action
• It remains in Base until the next unit dies and triggers its ability

Nuances:

• There is debate about whether the card ever technically enters the battlefield or goes directly to base, but this distinction does not matter for any card in set 1
• Playing Zhonya's from hidden cannot be reacted to because permanents auto-resolve when they are the last link on the chain
• The flip can be done preemptively before a unit dies, and Zhonya's will wait in base