If a unit with 'attacking/defending alone' ability enters showdown with multiple units, and then another unit is removed (e.g., via Fight or Flight), does the ability activate?

Ruling: Yes, passive effects like "attacking/defending alone" are constantly checked and activate immediately when their condition is met. Removing a unit from showdown to make Wielder of Water alone would give the +2 bonus.

Nuances:

• Effects that trigger "as a result of doing X alone" won't retroactively trigger in the same event if the unit becomes alone mid-showdown (like Mask of Foresight)