If my opponent plays Thousand Tail Watcher, can I kill it with damage in response before its 'When you play me' ability resolves?

Ruling: No, you cannot prevent Thousand Tail Watcher's ability from resolving by killing it in response. Once a unit is played, its 'When you play me' ability goes on the chain and will resolve even if the unit is killed before the ability resolves.

Sequence:

• Opponent plays Thousand Tail Watcher
• The 'When you play me' ability goes on the chain
• You can respond with damage effects (like Shakedown) to kill the Watcher
• The Watcher dies
• The 'When you play me' ability still resolves and takes effect

Nuances:

• Abilities and spells in Riftbound do not fizzle - they always resolve unless countered
• If an ability's target becomes invalid, the ability still resolves but may have no effect
• Units can only be prevented from triggering their 'When you play me' abilities if they are countered before being played (preventing them from entering play at all)
• The unit does not need to be alive for its ability to resolve