If a battlefield has one unit and one hidden unit, and the opponent plays Unchecked Power, can the hidden unit be flipped after the damage to prevent losing control of the battlefield, or must it be flipped before taking damage?

Ruling: The hidden unit must be flipped before taking the damage. You cannot flip it after damage to save it from being trashed when you lose control of the battlefield.

Sequence:

• Unchecked Power deals damage to the unit
• If the unit dies and you have no other units at the battlefield, you immediately lose control
• When you lose control, any hidden card at that battlefield is immediately placed into the trash

Nuances:

• There is no window to flip the hidden unit in reaction to losing control of the battlefield
• The hidden unit will either die from Unchecked Power (if flipped before damage) or be sent from the hidden zone to trash during cleanup (if not flipped)