How does Zhonya's Hourglass interact with Deathknell abilities in different timing scenarios?

Ruling: Zhonya's Hourglass is a replacement effect that prevents death entirely, so Deathknell abilities do not trigger when ZH is active. ZH does not use the chain because it is a replacement effect - it just happens.

Sequence:

• Scenario 1 (ZH face up before DK unit dies): ZH replaces the death, so DK doesn't trigger at all
• Scenario 2 (Unit dies to spell damage, then ZH flipped in response): If ZH is flipped after the DK ability has already triggered, it's too late - the DK unit is already in the trash by the time ZH resolves
• Scenario 3 (Unit dies during combat damage cleanup phase): Still awaiting official updates from Riot on this interaction

Nuances:

• ZH is not optional, so if it's face up it will always replace death
• The key distinction is whether ZH is active before the death occurs (prevents DK trigger) or after DK has already triggered (too late to save the unit)