Can you use Void Seeker on a unit that moves into an open (unoccupied) battlefield?

Ruling: Yes, you can use Void Seeker on a unit that moves into an open battlefield. Moving into an open battlefield starts a showdown (but not a combat), and once that showdown starts and you get focus, you can cast Void Seeker.

Sequence:

• Opponent moves to empty battlefield
• Opponent has focus and priority, meaning they can cast action or reaction spells
• If opponent passes focus and priority
• You can now play action spells to start a chain

Nuances:

• Moving into an open battlefield starts a showdown but does not start a combat
• Action spells (not just reactions) can be played during an open showdown if you have focus