If Teemo Strategist is revealed as a defender during a showdown and the opponent uses Gust to return him to hand before his 'When I defend' ability resolves, does the ability still trigger and resolve?

Ruling: The 'When I defend' ability triggers as soon as Teemo becomes a defender and remains on the chain even if Teemo is returned to hand. You can still look at the top 5 cards, but you won't deal any damage since Teemo is no longer at the battlefield.

Sequence:

• Teemo is revealed as a defender at the battlefield
• Teemo's 'When I defend' ability triggers and goes on the chain
• Opponent can react by playing Gust to return Teemo to hand
• The triggered ability remains on the chain and resolves
• You look at the top 5 cards as per the ability
• No damage is dealt because Teemo is no longer 'here' at the battlefield

Nuances:

• Triggered abilities are separate entities from the unit that triggered them, so removing the unit doesn't remove the ability from the chain
• The only way to remove an ability from the chain is to counter it
• You cannot prevent the ability from triggering in the first place since units resolve immediately when played/revealed, which immediately triggers their abilities
• You do as much as possible when resolving the ability even if the source unit is gone