Can you respond to Sona's end of turn effect, and does moving, killing, or bouncing her stop the effect?

Question

Accepted Answer

Yes. The controller may place Sona, Harmonious's end‑of‑turn triggered ability on the chain if she is at a battlefield when the Condition is checked; once it is on the chain, players can respond to it. Moving/killing/bouncing Sona, Harmonious before the Condition is checked (i.e., before the trigger is placed) can prevent the ability from being placed. Moving/killing/bouncing her after the triggered ability has been placed on the chain does not automatically stop the ability from resolving unless the ability specifically requires Sona to be present or to be a target, or unless the ability contains costs that must be paid during finalization.

At the end of the turn the condition (“if I'm at a battlefield”) is checked and, if true, the controller may place the triggered ability on the chain [383.3.e] [383.3.f.1]. Once the triggered ability is on the chain players may respond to it like any other chain item [383.3.c]. If Sona, Harmonious is moved/killed/bounced before that condition is checked, the ability simply won't be placed on the chain [383.3.e]. If she is moved/killed/bounced after the ability has been placed on the chain, that does not by itself cancel the ability; it will still resolve unless the ability's effect targets or otherwise depends on Sona (or includes a cost tied to her that must be paid during finalization) [359.3.f.3.a] [383.3.b.2].

At the Ending Step the game checks the trigger Condition ("if I'm at a battlefield"). If Sona, Harmonious is not at a battlefield at that instant, the ability is not placed on the chain [383.3.e]. If the Condition is true, the controller may choose to place the Triggered Ability on the chain. That choice creates a pending chain item and it is queued for finalization [383.3.f.1] [FAQ:unleashed#2]. During finalization the controller makes any necessary choices and pays any costs required by the triggered ability (costs inside instructions are treated as the base cost of the Triggered Ability and are paid during finalization) [383.3.b] [383.3.b.1]. Once the triggered ability is on the chain, players get priority and may respond to it like any other chain item [383.3.c]. When the triggered ability resolves, it will perform its instructions. Moving/killing/bouncing Sona, Harmonious after the trigger was placed does not automatically stop those instructions unless the instructions explicitly target or depend on Sona, Harmonious or the ability included a cost that wasn’t satisfied during finalization [359.3.f.3.a] [383.3.b.2].

If the triggered ability's effect specifically targets Sona, Harmonious (or other objects that can cease to be the same object by changing to/from a non‑board zone), then moving her off the board could affect target legality and the effect could be ignored or partially ignored on resolution [359.3.e.4] [359.3.e.5]. If the triggered ability includes a cost like “you may exhaust me to …”, that cost is part of the ability's base cost and must be paid when the triggered ability is finalized on the chain; if the cost cannot be paid at finalization because Sona, Harmonious is no longer available to fulfill it, the ability may not be finalized or the cost can't be paid [383.3.b] [383.3.b.1]. If the effect creates or places things "here" (relative to Sona) the relevant referent is determined when the triggered ability is created; moving her afterwards may not change the created referent (see examples in the rules about referents being captured at creation) [359.3.f.3.a]. If the triggered ability itself is somehow removed from the chain while resolving, it will stop executing immediately [359.3.e.15].

At the heart of this interaction is the timing and where the condition is checked. Sona, Harmonious's ability is written as an "At the end of your turn, if I'm at a battlefield, ..." triggered ability. That "if I'm at a battlefield" is part of the Condition that is checked when the trigger would be placed; the triggered ability is only put on the chain if that conditional is true at that moment [383.3.e]. When that Condition is fulfilled the controller may choose to place the triggered ability on the chain [383.3.f.1], and triggered abilities can be put on the chain in Closed or Open States on any player's turn — meaning once it is on the chain players have normal opportunities to respond to it [383.3.c]. Consequence: Opponents can respond to Sona, Harmonious's triggered ability after it is placed on the chain and before it resolves. If Sona, Harmonious is moved, killed, or bounced before the end‑of‑turn Condition is checked, she will not be at a battlefield when the Condition is fulfilled and the ability will not be placed on the chain at all [383.3.e]. If she is moved, killed, or bounced after the ability has been placed on the chain, that does not by itself cancel the ability — the chain item remains and will resolve unless the ability's text specifically requires Sona to be present or to be a target, or unless the ability had a cost tied to her that wasn't paid during finalization [359.3.f.3.a] [383.3.b.2]. For example, an ability that merely says "ready up to 4 friendly runes" does not target or rely on Sona at resolution, so it will still resolve even if she left the battlefield after the trigger was placed. Conversely, an ability that included "exhaust me to ..." would require paying that cost during finalization; if you cannot pay it (because Sona is gone), that affects whether the triggered ability can be finalized and thus what will happen [383.3.b]. Finally, note that if an ability depends on a referent like "here," that referent is generally captured when the triggered ability is created; moving the source after creation may not change that captured information [359.3.f.3.a].