If you enter an empty battlefield starting a non-combat showdown, and during that showdown your opponent moves a unit into the battlefield with an action, does it become a combat showdown or does the non-combat showdown end first?

Ruling: The non-combat showdown must be completed first. After it finishes, a combat showdown immediately begins with the person who moved their unit to the battlefield first as the attacker and the other player as the defender.

Sequence:

• Step 1: Complete the non-combat showdown that was already in progress
• Step 2: Immediately stage a combat showdown
• Step 3: The player who moved to the battlefield first becomes the attacker, the other player becomes the defender (in this scenario, the original player is the attacker and the opponent is the defender)