If an opponent plays Cull the Weak targeting my only unit, can I respond with Gust to return that unit to my hand, and what happens to Cull the Weak if I have no other units?

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Accepted Answer

Yes — you can play Gust in response to Cull the Weak (so long as the unit has 3 Might or less). Cull the Weak does not target; when it later resolves each player must kill one of their units. If you returned your only unit to your hand with Gust, you have no units to choose, so the instruction for you to kill a unit is ignored and you don’t lose anything. Your opponent still kills one of their units as normal.

You may play Gust in response to Cull the Weak to return your unit (if it has 3 :rb_might: or less) to your hand. Cull the Weak's text “Each player kills one of their units” does not target [355.10.e], so removing your unit before resolution simply means you have no unit to kill when the spell resolves. Because you have no unit then, the spell’s instruction for you cannot be completed and is ignored [359.3.e.6]. The opponent’s portion still resolves and they kill a unit they control.

Opponent plays Cull the Weak and places it on the chain. Because its text is “Each player kills one of their units,” it does not create targets at this time [355.10.e]. Before Cull the Weak resolves, you play Gust as a Reaction (its card text allows playing it any time). If the unit at the battlefield has 3 :rb_might: or less, Gust returns that unit to your hand. After Gust resolves and the unit is in your hand, Cull the Weak then resolves. As part of resolution, each player must choose a unit they control to kill (choices are made on resolution) [355.17]. You have no units to choose, so the instruction for you to kill a unit cannot be completed and is ignored [359.3.e.6]. Your opponent still chooses and kills one of their units.

If the unit has more than 3 :rb_might:, Gust cannot legally return it and you cannot use Gust to avoid Cull the Weak. If some other effect moved the unit to a non-board zone (trash/banish) before resolution, that object is no longer the same game object on the board; because Cull the Weak doesn’t target, the spell will still ask each player to kill a unit, but you still have no unit on the board to choose and so nothing happens for you. See the distinction between board vs non-board zone changes in target rules [359.3.e.4]. If you return the unit to your hand but another simultaneous effect creates a new unit for you before Cull the Weak resolves, you would be required to choose a unit you control to kill (the new unit) when the spell resolves. If both players have no units when Cull the Weak resolves, neither player kills anything; the spell resolves with no effect for either player.

Two separate principles decide the outcome here. First, Cull the Weak reads “Each player kills one of their units,” which by rule is not a targeted instruction — it asks each player to choose a unit to kill as the spell resolves rather than creating targets when the spell is placed on the chain [355.10.e]. Second, Gust is a Reaction that you may play before the spell resolves (its card text explicitly allows this). If you use Gust to return your only unit (and that unit is 3 :rb_might: or less so the play is legal), the unit leaves the battlefield and goes to your hand before Cull the Weak resolves. When Cull the Weak then resolves, each player is instructed to kill a unit they control; you have no units to choose and therefore cannot perform that instruction. Instructions that cannot be followed are ignored [359.3.e.6], so you simply don't kill anything. Your opponent, assuming they have at least one unit, will choose and kill a unit they control as the spell resolves. This line of reasoning relies on choices for that kind of instruction being made on resolution [355.17] and on the non-targeting nature of the spell [355.10.e].