Does damage from Iron Ballista persist until showdown combat damage calculation, allowing a lower might unit to kill a damaged unit?

Ruling: Yes, damage marks from Iron Ballista persist during combat and are only cleared after the combat resolves or at end of turn.

Sequence:

• Use Iron Ballista to deal 1 damage to a 3 might unit
• Attack their battlefield to initiate showdown
• The damage mark remains on the unit during combat
• A 1 might unit can kill the damaged 3 might unit during showdown

Nuances:

• Some effects like Zhonya protect can clear damage marks before combat ends