Can I use Diana, Lunari's ability on an open battlefield?

Ruling: Yes, you can use Diana, Lunari's ability on an open battlefield. Moving a unit to an open (uncontrolled and unoccupied) battlefield creates a non-combat showdown, which triggers Diana's "When a showdown begins here" ability.

Sequence:

• A unit moves to an open battlefield
• The battlefield becomes contested
• A non-combat showdown begins during cleanup
• Diana's ability triggers if she is present at that battlefield
• You may pay [1] to Predict and potentially draw a spell

Nuances:

• Non-combat showdowns occur when an empty battlefield becomes contested
• Moving to any battlefield you don't control starts a showdown, even if no enemy units are present