When Yasuo Remorseful's ability and a defender's ability (like Reavers Row) both trigger, does Yasuo have to choose his target before the defender chooses which unit to retreat?

Question

Accepted Answer

No — there is no automatic requirement that Yasuo - Remorseful choose a target before the defending player chooses which unit to retreat with Reaver's Row. Each triggered ability is placed on the chain and its controller makes choices (including target selection or whether to move a unit) during that ability's finalization; which choice happens first depends on the order the triggered abilities are finalized/placed on the chain.

When Yasuo - Remorseful's attack trigger and Reaver's Row's defend trigger both trigger, both triggered abilities are put on the chain. Each ability's controller chooses targets/choices when they finalize that triggered ability onto the chain (not necessarily at the instant the triggers were created). Therefore Yasuo - Remorseful does not automatically pick a target before the defender picks which unit to move; the order of those choices depends on which triggered ability is finalized first. If Yasuo - Remorseful's ability is finalized and chooses a target, and later the chosen unit is moved off the battlefield (to base) before Yasuo's ability resolves, Yasuo's instruction will check legality on execution and may mistarget or do nothing if the chosen unit is no longer a legal target for "an enemy unit here." [359.3.f.3] [FAQ:unleashed#2] [359.3.f.2] [359.3.e.5]

An attack event occurs with Yasuo - Remorseful attacking; that creates Yasuo's triggered ability "when I attack…" and simultaneously the defender's "when you defend here" trigger from Reaver's Row (if applicable). Both triggered abilities are placed on the chain as pending triggers. They will be finalized/placed onto the chain following the game's triggered-ability ordering rules (not provided in full here). See [FAQ:unleashed#2]. When a player finalizes one of those triggered abilities during finalization, that player makes the choices required by that ability (e.g., the controller of Yasuo - Remorseful chooses the target for his triggered ability; the defender chooses which friendly unit to move for Reaver's Row). See [FAQ:unleashed#2]. Which choice happens first depends on which triggered ability is finalized/placed on the chain first. If the defender finalizes Reaver's Row first they will pick which unit to move before Yasuo - Remorseful's controller picks a target; if Yasuo's controller finalizes first they will pick a target first. When Yasuo - Remorseful's triggered ability later resolves, the instruction will check whether the chosen target is still a legal "enemy unit here." If that chosen unit was moved off that battlefield (for example to base) prior to execution, Yasuo's instruction may mistarget or do nothing per [359.3.f.2] and [359.3.e.5].

If the defender moves the chosen unit to a non-board zone (hand, deck, banish) after it was chosen by Yasuo's triggered ability but before resolution, that object is no longer the same game object and the targeting relationship is severed — Yasuo's trigger will not affect it when it resolves. See [359.3.e.3]. If Yasuo's trigger was finalized choosing a unit and that unit is later moved to base (a board zone) before resolution, the chosen relationship remains but the instruction may be illegal because the unit is no longer “here”; the ability will then be unable to follow that instruction and will do nothing to that target. See [359.3.e.3] and [359.3.f.2]. If some effect in reaction transfers control of the chosen unit to Yasuo's controller (or otherwise changes whether it's an "enemy"), the targeting may be affected depending on whether the triggered ability referenced "enemy" from its trigger condition; refer to the rules explaining where words like "enemy" are referenced. See [359.3.f.3] and [359.3.f.2]. If there are specific local rules about the ordering of simultaneous triggers (for example, always active player first), that will determine which player makes their choices first. That ordering is outside the excerpt provided here.

Short answer: No — there is no blanket requirement that Yasuo - Remorseful choose his target before the defender chooses which unit to retreat with Reaver's Row. Both are triggered abilities that are created when the attack/defend event occurs; per the rules for triggered abilities, the triggers are placed on the chain and choices (including target selection or the choice to move a unit) are made when a triggered ability is finalized/placed on the chain, not necessarily at the instant the trigger was generated. See [FAQ:unleashed#2] and [359.3.f.3].

How this plays out in practice:
• Both the attack trigger from Yasuo - Remorseful and the defend trigger from Reaver's Row go on the chain when the attack/defend event happens. The game then follows its trigger-finalization/ordering procedure to decide which triggered ability is finalized/placed on the chain first. When a player finalizes one of those triggered abilities they make the choices required by that ability (for Yasuo, choosing the "enemy unit here" target; for the defender, choosing which friendly unit to move to base). This is explained in [FAQ:unleashed#2].
• Therefore whether Yasuo's controller chooses his target before the defender chooses which unit to move depends entirely on the order in which those triggered abilities are finalized (i.e., which gets to make choices first). If Yasuo's trigger is finalized first, he picks a target then the defender later chooses which unit to move; if the defender's trigger is finalized first, they pick and move a unit before Yasuo chooses his target.
• Be careful about what happens between choice and resolution: when Yasuo - Remorseful's triggered ability resolves it will "deal damage equal to my Might to an enemy unit here." The resolution checks legality on execution; if the chosen unit is no longer an eligible target (for example, it was moved off that battlefield so it is not "here" anymore), the instruction will be unable to affect that target and will do nothing to it. See [359.3.f.2] and [359.3.e.5].
• Note also that choosing a target for a triggered ability creates a targeting relationship so long as the object remains the same game object on the board; moving it between battlefields may gray out that relationship but keep it present, while moving it to a non-board zone severs the relationship entirely. See [359.3.e.3].

If you need a concrete resolution for a specific table: tell me which player’s triggers finalize first at your table (active player first or last), and I will give the exact order and the immediate outcomes for the choices and resolution.