Can you Gust Vayne when she enters a battlefield?

Question

Accepted Answer

Yes — you can play Gust to return Vayne as she enters a battlefield, provided she is a unit at a battlefield with 3 or less Might at the moment you play (and at the moment Gust resolves). If she is not a legal target (for example, her Might is >3, or she moves to a non-board zone before Gust resolves) then Gust will not affect her.

You may Gust Vayne when she enters a battlefield as long as she is a unit at a battlefield and has 3 or less Might when you target her and when Gust resolves. If she ceases to be a legal target before resolution (Might >3, moves to a non-board zone, or otherwise stops meeting the targeting restriction), she will not be returned.

Confirm Vayne is a Unit and has 3 or less Might as she is on the battlefield. Play Gust as a Reaction (you may do so when she is entering or immediately after she has entered, since Reactions can be played in response to actions and while things are on the chain). When Gust is played you target Vayne (she must be a legal target — a unit at a battlefield with Might ≤3). If Vayne remains a legal target when Gust resolves, return her to her owner's hand. If she is no longer a legal target (for example, her Might becomes >3, or she changes to a non-board zone before resolution), Gust will not affect her [359].

If Vayne has Might greater than 3 at the time you try to play Gust, she is not a legal target and you cannot choose her. If Vayne is moved to a non-board zone (hand, deck, void) before Gust resolves, she becomes a different object and will not be affected by Gust [359]. If Vayne is moved to Base (a board zone that is not a battlefield) after you target her with Gust but before Gust resolves, she is no longer a legal target for Gust (she won't be returned) per the legal-target checks on resolution [359]. If some other effect changes Vayne's characteristics (for example, raises her Might above 3) before resolution, she ceases to be a legal target and Gust will not return her [359]. If you play Gust in reaction to an ability that put Vayne onto the battlefield, you may still play Gust (Reactions can be played any time, per the card keyword). Whether Gust actually returns her depends on the legal-target checks when Gust resolves.

The card Gust is a Reaction that returns "a unit at a battlefield with 3 Might or less to its owner's hand." Reactions may be played in response to actions and abilities (the card’s [Reaction] keyword text allows playing it while spells and abilities are on the chain). To use Gust on Vayne when she enters a battlefield, two things must be true: she must be a Unit at a battlefield, and her Might must be 3 or less at the time you choose her and when Gust resolves. A unit entering a battlefield via a Standard Move or via a spell/ability is on the board as a unit at a battlefield, so you can target it with Gust as it enters (see [144] for Standard Move context and [444] for moves caused by spells/abilities). When you play Gust you create the targeting relationship; if Vayne later ceases to meet the targeting requirements by the time Gust resolves, that instruction will be ignored for that target per the legal-target resolution rules [359]. The FAQ clarification shows the distinction between moving to base (still 'on the board' but not at a battlefield) and moving to a non-board zone: a target moved to base may remain a chosen target for some spells, but it will not be a legal target for a spell that specifically requires "a unit at a battlefield" when the spell resolves, and if a target changes to a non-board zone the relationship is severed entirely [FAQ:unleashed#22] [359]. Therefore: yes you can Gust Vayne as she enters a battlefield, provided she is a legal target (Unit at a battlefield with ≤3 Might) when you play and when Gust resolves; otherwise Gust will not return her.