Can you react to Traveling Merchant's move trigger with Hidden Blade at reaction speed and kill him? Does he count as being at a battlefield when his move trigger goes on the stack?

Ruling: Yes, you can use Hidden Blade at reaction speed to kill Traveling Merchant when his move trigger goes on the stack, but only if the Hidden Blade was already hidden at that battlefield. However, killing him will not deny his discard/draw triggered ability.

Sequence:

• Traveling Merchant's triggered ability is added onto the chain
• You can then react to it with Hidden Blade (if it was hidden at that battlefield)
• Even if you kill Traveling Merchant, his triggered ability still resolves

Nuances:

• The showdown has not begun yet when the trigger happens, but Traveling Merchant is considered to be at the battlefield for targeting purposes
• The triggered ability on the chain is not contingent on Traveling Merchant being alive, so it resolves even if he is killed or bounced