Are units continuously checked for Attacker/Defender status during a Showdown, and how does this work for units like Blue Teemo and Yellow Shen that enter during combat?

Ruling: Units are continuously checked for Attacker/Defender status during a Showdown as part of the Clean-up check. When a unit like Blue Teemo is revealed as a REACTION during an open chain, its Defender trigger goes on top of the current chain.

Sequence:

• Units entering during a Showdown are checked for Attacker/Defender status during Clean-up
• If a unit is revealed as a REACTION while a chain is open, its trigger goes on top of the existing chain
• The trigger does not become pending in this scenario

Nuances:

• Pending status is primarily relevant when something is played while something else resolves (e.g., cards played as part of Promising Future's resolution)
• Even pending effects finalize onto the chain on top of any other potential effects already there