When Teemo Scout is revealed from hidden, can you respond to its on-play ability with Gust before the on-play resolves?

Question

Accepted Answer

Yes. After you play Teemo - Scout from Hidden, its “When you play me…” ability will trigger and be placed on the chain; an opponent may play Gust as a Reaction in response before that triggered ability resolves (and return Teemo - Scout to hand, preventing the buff from applying).

You may respond to Teemo - Scout being played from Hidden with Gust before the on-play triggered ability resolves. Playing Teemo - Scout from Hidden opens a chain item for the play and the triggered "When you play me" ability triggers and becomes a chain item that players can react to. If Gust returns Teemo - Scout to hand before the trigger resolves, the triggered instruction to give it +3 [M] will be unable to affect it and will be ignored when it resolves. [811.1.c.3] [355.5.b] [359.3.e.6] [359.3.e.5]

You play Teemo - Scout from Hidden; that Play opens a chain item because playing from facedown opens a chain. [811.1.c.3] When the play occurs, Teemo - Scout's "When you play me" ability triggers and becomes its own chain item (triggered abilities that trigger on play are placed on the chain and their choices/targets are made during finalization, not as part of the play). [355.5.b] While that triggered ability is pending on the chain but before it resolves, players may respond with Reactions (including the opponent playing Gust) because they can play reactions to spells/abilities on the chain. If the opponent plays Gust targeting Teemo - Scout (it is a legal target while it is a 1 [M] unit at a battlefield), Gust resolves first and returns Teemo - Scout to its owner's hand. When the original "When you play me" triggered ability subsequently resolves, its instruction to give +3 [M] to the unit cannot be applied to the unit in-play (it's no longer at that battlefield), so that instruction is ignored per the rules about instructions that can't be followed. [359.3.e.6] [359.3.e.5]

If some effect during the play immediately increases Teemo - Scout's Might above 3 before the opponent casts Gust, then Gust could no longer legally target it. See the targeting legality rules. [359.3.e.5] If Teemo - Scout's on-play text were worded as a play-effect rather than a triggered ability (e.g., as part of the resolution of the Play itself), the timing could be different. However, the printed wording "When you play me" is a triggered ability, so the above ruling applies. [355.5.b] If Gust is instead played from Hidden or from some other source with timing restrictions, ensure it is being played at a time Reactions are allowed; Hidden grants Reaction to the facedown card while facedown and when played from facedown. [811.6] If multiple reactions are played in response, normal chain ordering and finalization rules determine resolution order and legality checks at each resolution step.

When you play Teemo - Scout from Hidden, that act of playing it opens a chain item because playing a card from facedown opens a chain. [811.1.c.3] The printed text on Teemo - Scout is "When you play me, give me +3 :rb_might: this turn," which is a triggered ability that triggers when the unit is played. Triggered abilities that trigger on being played are placed on the chain as separate items; they do not require their choices or targets to be made as part of the play itself. [355.5.b] Once that triggered ability is on the chain, players may play Reactions in response before it resolves. Gust is a Reaction and may be played in response to the triggered ability going on the chain. [811.6] If Gust returns Teemo - Scout to its owner's hand before the triggered ability resolves, the instruction to give +3 Might cannot be applied to the unit on the battlefield and thus will be ignored when the trigger resolves. This follows the rules that instructions that can't be followed are ignored and that targets/instructions that become illegal are unaffected or ignored as appropriate. [359.3.e.6] [359.3.e.5] Therefore, an opponent can indeed use Gust to remove Teemo - Scout before its "When you play me" buff resolves.