When do Deathknell triggers resolve during showdown combat, and can players play spells between Deathknell resolution and healing/scoring?

Ruling: There is no confirmed official answer. The unconfirmed consensus is that Deathknell happens between healing and scoring (contest clearing), and players can only react at this point while there is an item on the chain.

Nuances:

• According to the retired FAQ, Deathknell happened after healing
• This topic lacks official confirmation and remains disputed