Can Zhonya's Hourglass be played hidden at base to recall a battlefield minion when a champion dies, or does it need to be on the same battlefield?

Ruling: You cannot hide cards at base. Zhonya's Hourglass must be played face up to your base, where it can save your next unit to die anywhere on the board.

Nuances:

• Gear cannot be at battlefields, which makes Hourglass unique as a Hidden card
• If you hide Hourglass at a battlefield and then play it from hidden, it gets played to base rather than the battlefield it was hidden at
• Once at base, it can save your next unit to die anywhere on the board