In a 4-player free-for-all, when attacking a held battlefield and starting a Showdown, can players other than the attacker and defender participate in the combat?

Ruling: Only the two players with units at the battlefield are initially relevant players in the Showdown. However, these relevant players can invite other players to participate when they have Focus or Priority.

Sequence:

• Only attacker and defender are initially relevant players
• When a relevant player has Focus or Priority, they may attempt to invite an outsider
• The invited player may accept or refuse
• If they accept, they must play something and become a relevant player for the Showdown, able to play cards later in that same Showdown
• If they refuse, the inviting player loses the ability to invite that specific player for that Priority/Focus

Nuances:

• Third players cannot independently decide to play reactions; they must be invited
• You can have Priority without Focus and still invite other players
• If you fail to invite a player (they refuse), you cannot invite that same player again during that same Priority/Focus window