Can I react to my opponent's Quick-Draw on the stack?

Ruling: You can react to the Quick-Draw triggered ability, but not to the Gear card itself being played. The Gear enters play immediately, then its "When you play this, attach it to a Unit you control" triggered ability goes on the chain, which you can respond to with Reactions.

Sequence:

• Opponent plays the Quick-Draw Gear card (it has [Reaction] timing permission)
• The Gear enters play at opponent's base immediately (does not use the chain)
• Quick-Draw triggered ability is placed on the chain and targets a unit
• You gain priority and can play Reactions to respond
• Chain resolves in Last-In, First-Out order

Nuances:

• You cannot counter the Gear card itself since it doesn't use the chain to enter play
• You can only counter the Quick-Draw triggered ability if your counter specifically targets abilities on the chain
• If you remove the targeted unit before the ability resolves, the Quick-Draw ability fails and the Gear remains unattached at the opponent's base
• Quick-Draw attachment is mandatory if a legal target exists (not optional)
• During Showdown, playing Quick-Draw Gear doesn't end the opponent's focus; play continues after the chain resolves