When Possession is played as the second card of the turn targeting Darius Trifarian, does Darius see it as the second card played and trigger his ability, or does he fail to see it because he was under opponent's control when Possession started resolving?

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Accepted Answer

No — If your opponent plays Possession as their second card targeting Darius - Trifarian, Darius - Trifarian will not see that play and will not trigger for your opponent. A triggered ability’s trigger condition looks at the controller relevant to the ability at the moment the triggering event happens; changing control later (during resolution) does not make the ability retroactively trigger for the new controller. [FAQ:unleashed#1] [359.3.f.4]

When Possession is played as the second card of a turn targeting Darius - Trifarian, Darius - Trifarian only triggers if its controller is the player who actually played that second card at the moment the card was played. If the opponent played the second card but did not control Darius - Trifarian at that instant, Darius - Trifarian does not trigger. If instead the controller of Darius - Trifarian was the one who played the second card, the Darius trigger would be placed on the chain and will resolve even if control of the unit changes while the trigger is on the chain. [FAQ:unleashed#1] [359.3.f.4]

Player B plays Possession as their second card, targeting Darius - Trifarian who is controlled by Player A at that moment. The event “Player B plays their second card” occurs. Triggered abilities that read “When you play your second card…” are checked with respect to the controller of the ability at the instant the event happens; Darius - Trifarian is controlled by Player A, so it does not see Player B’s play and does not trigger. [FAQ:unleashed#1] Possession resolves: it first takes control of the chosen unit and then recalls it (send it to its base). Any instructions that cannot be executed are ignored as much as possible. If an ability had already triggered earlier it would still resolve on the chain even if control changed. [359.3.e.11] [359.3.f.4] If instead Player A (the controller of Darius - Trifarian) had been the one to play the second card, Darius - Trifarian’s trigger would be placed on the chain and will resolve normally even if control changes before that trigger resolves. [359.3.f.4]

If some earlier effect already made Player B the controller of Darius - Trifarian before they played Possession, then Darius - Trifarian would be controlled by Player B at the moment they played their second card and would trigger. If a reactive spell or effect stole control of Darius - Trifarian in response to the play of Possession (i.e., before the Possession was played or while it was being finalized), the timing of when control changed relative to the play matters. Only control at the instant the second-card event occurs matters for whether the trigger is placed on the chain. [FAQ:unleashed#1] If Darius - Trifarian ends up off the board (recalled) before any later instruction needs its on-board information, checks for its Might/location/etc. may return null as described by [359.3.e.12]. If a player gains control of a triggered ability itself (not the source unit) and makes new choices for it, that can change how the trigger resolves—see examples in [359.3.f.4].

Short answer: Darius - Trifarian will not trigger for the opponent's play of Possession unless the opponent already controlled Darius - Trifarian at the instant they played that second card. Reasoning: Triggered abilities are split into trigger condition and effect; the trigger condition “When you play your second card in a turn” is evaluated with respect to the controller of the ability when the triggering event happens. The provided triggered-ability sequencing guidance indicates which pieces are the trigger condition and thus are checked at the moment of the event, so “you” in that condition refers to the unit’s controller at that instant [FAQ:unleashed#1]. In your scenario, when Player B plays Possession as their second card, Darius - Trifarian is still controlled by Player A, so the Darius ability’s trigger condition (“When you play your second card…”) is not satisfied for that unit and no trigger is placed on the chain for Player B.

What about control-changing during resolution? If Darius - Trifarian had triggered (because its controller actually played the second card), that trigger being placed on the chain is unaffected if control later changes while the trigger waits to resolve; a triggered ability already on the chain continues to resolve according to the information the trigger references, as shown in the Yasuo example where a unit changing controllers after the trigger was placed does not retroactively invalidate the trigger ([359.3.f.4]). Conversely, if the unit is moved off the board and a later instruction needs on-board information, checks can return null and calculations based on them are ignored ([359.3.e.12]).

Therefore: unless your opponent already controlled Darius - Trifarian before playing Possession, the opponent’s play of Possession as their second card will not cause Darius - Trifarian to trigger for them. If you need a ruling for a specific board state where additional control changes or reactions occurred earlier in the turn, give that exact sequence and I can apply the same rules to that precise timing.