What happens if a third player plays Zenith Blade to move their unit to a battlefield where two other players are already in combat?

Ruling: Zenith Blade's movement is optional, so you cannot choose to move your unit to a battlefield where two other players are already in combat, since only 2 players can be in combat at the same time.

Nuances:

• If Zenith Blade were a required movement effect, you would not be able to play the card at all because it would create an illegal game state (3 players at 1 battlefield)
• The concept of being 'invited' to interact has been removed; all players can interact