When playing Tideturner to base targeting Ember Monk at a battlefield where you control a hidden card, do you need to reveal the hidden or do you maintain control because the effect is instantaneous?

Ruling: You do not lose control of the battlefield. Cleanups (like revealing hidden cards when losing control) do not happen during the resolution of spells and abilities.

Nuances:

• If cleanups did happen during resolution, playing this on an opponent's turn could allow you to score a conquest point, which would be problematic
• There is no explicit rule preventing cleanups during resolution, but judges rule this way to avoid problematic interactions