Can Ekko's Deathknell ability untap runes during a showdown in time to kill a damaged opponent's unit before damage is cleared?

Ruling: No, you cannot untap runes and use them to kill damaged units before damage is cleared. By the time Ekko's Deathknell triggers, the showdown has already ended.

Sequence:

• Units are killed first
• Damage is cleared second
• There is no opportunity to play cards between these steps

Nuances:

• Once you reach damage calculation, do the resolution step, and perform the cleanup, nothing else can be done about the showdown