Does Teemo's new text still trigger when played from hidden during a showdown?

Ruling: Yes, Teemo still triggers when played from hidden during a showdown because he is assigned as a defender when played to the battlefield, which triggers his "when I defend" ability.

Sequence:

• Teemo is played from hidden to the battlefield during a showdown
• Teemo is assigned as a defender
• His "when I defend" ability triggers and enters the chain
• The ability targets an opposing unit at the battlefield

Nuances:

• "When I attack" and "when I defend" triggers are not exclusive to the start of a showdown
• These triggers happen whenever a unit is assigned attacker or defender, which can occur in the middle of a showdown if a unit enters the battlefield