LeBlanc, Deceiver interaction with gusting. If I react to the initial trigger and gust all valid targets, what happens? If I react to the reflexive trigger and gust the chosen target, what happens?

Both lines end the same way for the token — it still enters, stays a 0 [M] Reflection, copies nothing, and still picks up Temporary. The difference is only what your Gust is aimed at.

Reacting to the initial "when you conquer or hold" trigger cannot stop the token. That trigger targets nothing — LeBlanc's controller already paid the discard/exhaust costs at finalization — so Gusting the units there only strips away the copy candidates. When the reflexive trigger ("Then do this: It becomes a copy of another unit there") is created, there's no legal "another unit there" left, so nothing is copied and the token sits as a 0 [M] Reflection (it still gains Temporary — FAQ #11514). Two caveats: Gust only reaches 3 Might or less, so any 4+ Might unit at that battlefield still gets copied, and you can't Gust the Reflection itself here because it doesn't exist yet.

Reacting to the reflexive trigger is the cleaner line: Gust resolves first (LIFO), sending the already-chosen copy target to hand — a non-board zone, which severs the targeting relationship — so the copy instruction mistargets and does nothing, per Rule 359.3.e.7. The token is already on the board as a 0 [M] unit and keeps its granted Temporary, so it dies at the start of its controller's next Beginning Phase, before scoring.

If you'd rather kill the token outright, Gust it instead in that second window — it's a legal target while still 0 [M], and a token sent to hand ceases to exist, leaving nothing to copy and no Temporary to matter.