After playing Hidden Blade on an enemy unit with Deathknell, who gets priority first after the Deathknell trigger finalizes?

Ruling: The player controlling the Deathknell effect gains priority, as they control the newest item on the chain after the trigger is finalized during cleanup.

Sequence:

• Player A plays Hidden Blade and starts a chain
• Chain finalizes and executes, both players pass
• Chain resolves and Hidden Blade effect executes
• Cleanup takes place upon removal of last item on the chain
• Deathknell triggers on cleanup and is added to the chain
• Deathknell is finalized within cleanup
• Chain goes to step 1 and finalizes
• Player controlling the Deathknell effect (newest in chain) gains priority

Nuances:

• Finalizing does not modify priority in general, but when a new effect is added to the chain during cleanup, the controller of that newest effect gains priority