Can you react to LeBlanc Deceiver? If so, when?

Yes, you can react to LeBlanc, Deceiver's ability. Because her ability is a triggered ability ("When you conquer or hold..."), it uses the chain, creating a Closed State where players can add [Reaction] cards.

According to RiftJudge FAQ #10236, there are two primary windows where you can play reactions (such as Gust) to interact with her ability:

The Timing Sequence

1. Trigger Window: When you trigger the ability (by holding or conquering), it is placed on the chain. Players have a window here to play [Reaction] cards before the ability begins to resolve.
2. Resolution & Reflexive Trigger: The ability resolves, creating the Reflection unit token.
   • Note: You cannot react to the unit entering play, as units enter the chain and finalize immediately.
   • However, after the token is created, a reflexive trigger ("It becomes a copy of another unit there...") is placed on the chain as a separate effect.
3. Reflexive Window: Players have a second window to play [Reaction] cards in response to this reflexive trigger before the Reflection token officially becomes a copy of another unit.

Important Considerations:

• Costs: As established in RiftJudge FAQ #10107 and #8686, discarding a card and exhausting LeBlanc are costs that must be paid when you choose to activate/trigger the ability. If you cannot pay these (e.g., you have no cards in hand), the ability cannot be placed on the chain at all.
• Targeting: Per RiftJudge FAQ #9613, if you intend to move or remove a target with a reaction, you must be aware that targets for triggered abilities are chosen when the ability is placed on the chain. If a unit (like the Reflection token) does not yet exist when that ability is placed, it cannot be chosen as a target for that specific ability.