If Fiora (Peerless Duelist) is defending at Reavers with a hidden Fog of War, and 2 cards attack her, can you play the hidden Fog of War on defend triggers to make it one-on-one and trigger Fiora's ability?

Ruling: Fiora's ability does not trigger. Her trigger condition requires her to be attacking or defending one-on-one at the time attack/defend triggers are evaluated. Since she is not one-on-one when triggers are initially checked, her ability does not go on the chain at all, and playing Fog of War afterward cannot retroactively create the trigger.

Sequence:

• Combat is declared with 2 attackers against Fiora
• Attack/defend triggers are evaluated and added to the chain
• Reavers triggers (if applicable), but Fiora does not trigger because she is not one-on-one
• After initial triggers are on the chain, Fog of War can be played
• Fog of War resolves and removes one attacker, but this does not allow Fiora's trigger to be added retroactively

Nuances:

• It is more accurate to say Fiora's ability "doesn't trigger at all" rather than being "missed" - a missed trigger infraction would only apply if the trigger condition was met but the player failed to acknowledge it
• Reaction speed of Fog of War does not matter; triggers are evaluated before players can add reactions to the chain
• The timing of when triggers are evaluated versus when reactions can be played is the key distinction