If my only unit at a battlefield with Merchant and hidden Tideturner is Charmed to my opponent's battlefield, can I activate Tideturner to move the Merchant back, or does it fizzle when Charm resolves?

Ruling: You won't have a window to activate Tideturner. You lose the battlefield as soon as you don't have a unit there, unless it's contested.

Sequence:

• Charm resolves and moves the Merchant to the opponent's battlefield
• You immediately lose control of the battlefield (since you have no units there and it's not contested)
• Tideturner cannot be activated because you no longer control the battlefield