If I have a 4-power unit at a battlefield with Mask of Foresight in my base and a hidden unit (Tideturner) at that battlefield, when my opponent moves a unit into the battlefield, does the +1 buff from Mask of Foresight apply before I reveal the hidden unit as a reaction?

Ruling: Yes, the +1 buff from Mask of Foresight can apply before you reveal the hidden unit, making your original defender a 5-power unit. However, this depends on when you choose to reveal your hidden card.

Sequence:

• Your opponent moves a unit into the battlefield
• Mask of Foresight trigger condition is met (your unit is alone)
• You can let the Mask of Foresight trigger resolve, boosting your lone unit's Might by +1
• After the trigger resolves, you can then reveal and play the hidden unit as a reaction

Nuances:

• If you reveal the hidden unit before reaching the trigger point (before the showdown starts and before your unit is designated as an attacker/defender), Mask of Foresight won't boost because the unit is no longer alone when designated