Does Master Yi's passive ability (+2 might to lone defenders) apply immediately when a showdown begins, or only during combat resolution?

Ruling: Master Yi's passive ability grants +2 might to a lone defender immediately when the combat showdown begins, before any actions are taken. This is a passive effect that cannot be reacted to and applies as soon as the conditions are met.

Sequence:

• Opponent moves unit to battlefield with a defender
• Combat showdown begins
• Master Yi's passive immediately grants +2 might if only one defending unit is present
• Action chain begins (damage spells and other actions must account for the might increase)

Nuances:

• This is a might increase, not a buff token (the term "buff" has a specific mechanical meaning in Riftbound referring to buff tokens)
• The ability is always active while its conditions are met - if a unit is removed during the showdown leaving only one defender, that defender immediately gains +2 might
• Similar passive abilities like Assault and Shield also activate immediately when showdown begins