My opponent plays Leblanc and conquers a battlefield. They use their leader ability to make a Reflection token and discard a card for it. If I react with a Gust, will the Reflection token still be created?

Yes, the Reflection token will still be created, but it will not be able to complete the copy effect.

This interaction is covered by RiftJudge FAQ #10346, which explains that because Riftbound effects do not "fizzle," they continue to execute instructions as much as possible even if a target is removed.

Chain Sequence

1. Chain Item 1: The Deceiver ability (triggered by conquering).
2. Chain Item 2: Gust (played as a reaction).

Since the chain resolves in Last-In, First-Out (LIFO) order, your Gust resolves before the Deceiver ability.

Resolution Order

1. Gust Resolves: The target unit you chose is returned to its owner's hand. It is no longer at the battlefield.
2. Deceiver Ability Resumes: The ability continues to execute its remaining instructions:
   • "Play a ready Reflection unit token there": This instruction succeeds. A 0 [M] Reflection token enters the battlefield.
   • "Then do this: It becomes a copy of another unit there": This instruction attempts to resolve. Because the unit you originally intended to target (or the unit the opponent intended to copy) is no longer at that battlefield, this effect cannot be applied.
   • Result: Per the "do all you can" rule, the ability skips the impossible instruction. The Reflection token remains on the battlefield as a base 0 [M] unit without the rules text or stats of another unit.

Disclaimer: This ruling is based on the official RiftJudge FAQ #10346 regarding similar interaction with the Deceiver ability and unit removal.