Can you play an action (like Hextech Ray) in response to an opponent conquering an empty battlefield (e.g., targeting a Daring Poro)?

Ruling: Yes, you can play actions during the showdown that occurs when a unit moves to contest an empty battlefield. Note that while this creates a showdown, it is not a combat.

Sequence:

• When a unit moves to a battlefield not controlled by its controller, that battlefield becomes contested
• A showdown ensues even if the battlefield was previously empty
• During this showdown, you can play actions like Hextech Ray

Nuances:

• The showdown triggered by moving to an empty battlefield is not considered a combat
• A battlefield becomes contested when units move to it if it's not controlled by the controller of those units, even if no opponent units are present