Can a player play Rebuke (an action speed spell) on an attacking unit during a showdown after all their own units have been removed from that battlefield?

Ruling: Yes, a player can play Rebuke on an attacking unit even if they have no units remaining at that battlefield. Showdowns, once started, continue as normal until both players pass focus in succession.

Nuances:

• This applies whether one unit or all units are removed from the battlefield
• Players will always get an opportunity to play actions during a showdown
• The showdown does not end abruptly when one side has no units remaining