Deathknell

A Deathknell ability is added to the chain as a pending item before the dying permanent moves to the trash.^[808.1.d.2] Before the permanent leaves the board, the game records its location, attributes, and other information needed by its ability.^[808.1.d.3] If the permanent's death is replaced and it is not sent to the trash, the pending ability is removed from the chain.^[808.1.d.1] Each instance of Deathknell triggers separately and creates its own pending item.^{[808.2][808.2.a]}

After the cleanup finishes. The ability becomes a pending item before the unit moves to the trash.^{[323.4][323.5][808.1.d.2]} The remaining cleanup steps are then completed before that pending ability can be finalized.^[334]

During a combat cleanup, this means surviving units are healed before the Deathknell ability is finalized or resolved.^[466.1.a.1] After the cleanup, the ability is finalized, any required targets are chosen, and players receive priority before it resolves.^{[334.2][337.4]}

It depends on when the unit is killed and what kind of chain item caused it.

If a unit is killed to pay a cost, the kill happens while the card or ability is being finalized.^{[357.2][404.1]} The Deathknell ability becomes pending above that chain item.^[808.1.d.2]

If the original item is a spell or an ability that does not add resources, the pending Deathknell ability is finalized before play continues.^{[359.3.b][406.3]} Because it is newer on the chain, the Deathknell ability resolves before that spell or ability.^[340.1]

If the original item is a unit, gear, or ability that adds resources, it resolves immediately when finalized, before the pending Deathknell ability is processed.^[337.2] The Deathknell ability resolves afterward.

If a resolving card or ability kills the unit, that chain item continues resolving without interruption.^[354.3] The Deathknell ability becomes pending, but it cannot be finalized until the current chain item finishes resolving.^[334.2] The killing card or ability therefore finishes before the Deathknell ability can resolve.