Does Thousand-Tailed Watcher's ability start a chain and can it be responded to with reactions?

Ruling: Thousand-Tailed Watcher has a "When you play me" triggered ability that uses the chain and can be responded to with reactions.

Nuances:

• The key difference between triggered abilities (that use the chain) and static abilities (that don't) is the usage of "When" vs "While" in the ability text
• When playing Watcher, you must announce the trigger or you risk missing it if an opponent points it out later