When a unit with a triggered 'when you play' ability is played during chain resolution, does it go on the chain immediately after that chain link resolves? And when does a deathknell trigger resolve during combat?

Ruling: When you play a unit with a triggered ability during chain resolution, after that chain link completely resolves, the triggered ability goes on the chain as a new link. Deathknell triggers do not wait for combat to fully end - they are finalized onto the chain during the special cleanup that happens within combat cleanup.

Sequence:

• Combat damage is dealt
• Special cleanup occurs (deathknell unit dies from damage and adds trigger as pending, then trigger is finalized onto the chain)
• Chain created by special cleanup resolves
• Contested is cleared from battlefield (this happens after the special cleanup)
• Combat officially ends

Nuances:

• Chains can intercede game steps
• Reactions to deathknell can still happen before contested is cleared and control is established (but after combat damage)
• Combat cleanup is not itself a cleanup - it's the steps of ending combat, which includes a special cleanup
• Clearing contested from the battlefield is a step of combat cleanup that occurs after the special cleanup, not part of the special cleanup itself