When does Teemo's 'when this defends' trigger get added to the chain, and can it trigger twice if Teemo is revealed from Hidden in response to an earlier trigger?

Ruling: When I Attack and When I Defend triggers are added to the Initial Chain during a combat showdown, before the attacker gets Focus and Priority. If you reveal Teemo from Hidden as a Reaction to an earlier trigger (like Merchant's ability), Teemo will trigger his ability once when revealed, then trigger again separately during the When I Defend step of the showdown, resulting in a double trigger.

Sequence:

• Merchant's ability is added to the chain
• If you reveal Teemo from Hidden in response, Teemo triggers his ability
• Both triggers resolve
• Move to Showdown
• When I Attack triggers are added to the Initial Chain and resolve
• When I Defend triggers (including Teemo's) are added to the Initial Chain and resolve
• Attacker gets Focus and Priority for Actions

Nuances:

• Teemo is not meant to get a double trigger in general (per devs), but this specific scenario allows it because they are separate trigger instances
• Teemo is a complicated unit that devs have said will be getting slightly adjusted