If a unit kills a deathknell creature, do the units heal before the deathknell goes off?

Question

Accepted Answer

No — Deathknell triggers are placed on the chain before the dying permanent is moved to the Trash, but they do not automatically resolve before other triggers. Any "when you kill a unit" or similar triggers caused by that kill are also placed on the chain during the same cleanup and will resolve in the chain order. Whether the killer heals before the Deathknell resolves depends on the order the pending triggers are placed on the chain, not on an automatic heal-before-Deathknell rule.

When a unit kills a permanent with [Deathknell], that Deathknell is added to the chain as a Pending Item before the card is moved to the Trash [808.1.d.2]. In a Cleanup kill, Deathknells are added during the Cleanup's outstanding tasks (Task 3a) and then the killed units are moved to the Trash (Task 3b) [323.4] [323.5]. Kill-based triggers that care about "when you kill a unit" are attributed to the appropriate action and are likewise placed on the chain by the same process [428.5.c]. Because both kinds of triggers are pending on the chain, resolution order (and thus whether a heal resolves before a Deathknell effect) depends on the order the pending triggers are placed on the chain and any choices the controllers make when ordering their triggers [808.1.d.2] [428.1.a.1.b] [808.2]. There is no rule that automatically makes healing resolve before a Deathknell.

Damage is marked and Cleanup begins because a unit has damage ≥ its Might. During Cleanup Task 3a, any units with Deathknell that have lethal damage place their Deathknell triggers on the chain as Pending Items; note their attributes before finalization [323.4] [808.1.d.2]. At the same point (Cleanup), kill attribution is determined for the damage that caused the kill, so any trigger that cares about "when you kill a unit" is likewise recognized and placed on the chain [428.5.c]. During Cleanup Task 3b the killed units are moved to their owners' Trash [323.5]. All pending triggers (including Deathknell and any kill-based healing triggers) now exist on the chain and will resolve in whatever order the pending items were placed and ordered by their controllers [808.1.d.2] [808.2]. Therefore, whether the healer resolves before the Deathknell depends on the trigger ordering on the chain; there is no built-in rule that healing resolves before Deathknell.

If the dying permanent is not actually sent to the Trash (for example its Kill is replaced by a recall), the Deathknell will not occur [808.1.d.1]. If multiple Deathknell instances (or other triggers) are created, the controllers choose ordering for their own triggers when adding them to the chain [808.2]. Effects like Karthus - Eternal that cause Deathknells to trigger additional times will place additional Deathknell triggers on the chain, potentially changing the ordering and outcomes. If the kill was the result of an explicit Kill Instruction (not Cleanup), the Deathknell is still added to the chain before the unit is moved to the Trash [428.1.a.1.b].

When a Permanent with [Deathknell] dies, the Deathknell is functionally "When I die, [Effect]" and its trigger is added to the chain as a Pending Item before the card is moved to the Trash due to a Kill Instruction or Cleanup [808.1.d.2]. In a Cleanup situation the rules explicitly place Deathknell triggers during Cleanup Task 3a, noting the unit’s attributes before finalizing the trigger, and then in Task 3b the units are killed and placed in the Trash [323.4] [323.5]. Kill-based triggers that look for "when you kill a unit" are attributed to the action that caused the kill (for Cleanup kills, attribution goes to the spell or ability that dealt the damage immediately prior to the Cleanup) and therefore are likewise recognized and placed on the chain as pending at that time [428.5.c]. The result is that both Deathknell triggers and any "you killed a unit" healing triggers are put on the chain at the same point in the resolution sequence [323.4] [808.1.d.2]. Once they are pending on the chain, they will resolve according to the order in which the pending triggers were placed and any ordering choices controllers make when placing their triggers. For multiple instances of Deathknell on a permanent, the controller chooses the order to add those triggers to the chain [808.2]. Because placement and ordering on the chain determines which triggered effects resolve first, there is no automatic rule that makes the killer heal before the Deathknell resolves. Whether the heal resolves before the Deathknell depends entirely on the pending-trigger ordering. Examples from the supplied card data: Kog'Maw - Caustic's Deathknell would be placed on the chain before it moves to the Trash; if the killing unit had "When you kill a unit: heal X" that heal trigger would also be placed on the chain at the same time, and the two triggers would resolve in whatever order they were placed on the chain. Finally, note that if the death is replaced (e.g., a recall prevents the card from going to the Trash), the Deathknell will not occur [808.1.d.1].