Can Zhonya's Hourglass be played hidden in your base, or does it have to be played at a battlefield?

Ruling: You cannot play Hidden cards in your base. Zhonya's Hourglass must be played Hidden in a battlefield you control, or it can be played in your base by paying its cost normally (not Hidden).

Nuances:

• If Zhonya's is Hidden in a battlefield, it only applies to that battlefield when you react with it
• If Zhonya's is in your base (played normally), it will prevent the death of the next friendly unit killed no matter what battlefield