Can you play a card in a showdown after damage is dealt but before combat ends?

Ruling: You can only play cards after combat damage if there is a triggered ability that results from the combat damage. If no triggered ability occurs, the showdown ends immediately.

Sequence:

• Combat damage is dealt
• All units heal
• If triggered abilities exist from the damage, they are added to the chain and players can respond
• If no triggered abilities exist, the showdown ends

Nuances:

• A common example is flipping a hidden Teemo in response to a Deathknell trigger to stage a new showdown
• Effects like Kog'Maw's triggered ability are added to the chain after units have already healed, so he cannot finish off units damaged in combat