Does Mask of Foresight trigger when a unit with Challenge initiates a fight, or only during combat in showdowns?

Ruling: Mask of Foresight only activates during combat, which occurs when units from 2 players become present at a battlefield. Challenge does not create a combat, so Mask of Foresight does not trigger from Challenge fights.

Nuances:

• Mask of Foresight will not activate during an open showdown (when you move to a battlefield without any units)