When Icathian Rain triggers multiple times and causes a unit with Deathknell (like Watchful Sentry) to die on the first trigger, does the Deathknell create a pending chain or can it be added to the existing chain before the remaining Rain triggers resolve?

Ruling: Deathknell will be added to the existing chain after the first instance of the Rain trigger resolves, allowing it to resolve before the remaining Rain triggers.

Sequence:

• Icathian Rain creates multiple reflexive triggers on the chain
• First Rain trigger resolves, killing the Watchful Sentry
• Deathknell trigger is added to the chain between the reflexive triggers
• Deathknell resolves (drawing a card)
• Remaining Rain triggers resolve

Nuances:

• The key is that between reflexive triggers, there is time for new triggers to be added to the chain rather than creating a pending chain