If my opponent uses Charm to move my only unit from a battlefield where I have a Hidden card, does my Hidden card stay in play if I no longer control that battlefield?

Ruling: No, if you do not control the battlefield, the hidden card is immediately trashed.

Sequence:

• The unit is moved by Charm
• You lose control of the battlefield
• Cleanup step 5 occurs (cleanup happens anytime a move is completed)
• The hidden card is trashed

Nuances:

• You can use a reaction to reveal the hidden card before it gets trashed
• If the hidden card is Zhonya's, revealing it will play it to the battlefield it was hidden at, but since gear can't exist at battlefields, it immediately gets recalled to base
• If the charmed unit dies at its new location, Zhonya's will save it (assuming no other units die)