When my opponent equips a gear, can I react with Gust?

Yes, you can react to your opponent equipping a gear with Gust, provided the gear is being attached using the Equip ability and the target unit meets the criteria for Gust.

Why you can react

According to Rule 818.1, Equip is an activated ability. Activating an ability follows the same process as playing a card: the ability is placed on the chain, which creates a Closed State (Rule 150.2.a). Because the ability is on the chain, it creates a window for players to respond with reactions before the ability resolves.

Note: If the gear is simply being played to the battlefield (not using an Equip ability), it enters the chain and resolves immediately, which would not give you a window to react to the attachment.

The Sequence

1. Activation: Your opponent activates the Equip ability on their gear, targeting a unit.
2. Chain Starts: The Equip ability is placed on the chain.
3. Priority: The state becomes Closed. You have the opportunity to play a [Reaction] card.
4. Your Response: You play Gust (which has the [Reaction] keyword) targeting the same unit.
5. Resolution (LIFO - Last In, First Out):
   • Gust resolves first: It checks the target. If the unit has 3 might or less, it is returned to your opponent's hand.
   • The Equip ability then attempts to resolve. Since the target unit is no longer on the battlefield, the target is now illegal. The ability "whiffs" (resolves with no effect), and the gear remains unattached.

This is based on the interaction mechanics for activated abilities as established in RiftJudge FAQ #9560 and FAQ #10323.