Can a defending unit's activated ability be used during a showdown when the defending player has priority but not focus?

Ruling: No, activated abilities can only be played at base speed by default, which means during your turn, out of showdown, and with an empty chain. They cannot be used during a showdown even if you have priority.

Nuances:

• "Controlling player's turn" means only during your turn
• "Neutral" means out of showdown
• "Open" means empty chain
• All three conditions must be met to use an activated ability at base speed by default