How does Zhonya's Hourglass interact with Icathian Rain when a unit takes lethal damage? Why doesn't Zhonya's fully save the unit from all the damage?

Ruling: Icathian Rain creates six separate damage triggers on the chain. When Zhonya's Hourglass saves the unit from the first lethal damage and recalls it to base, the remaining triggers continue to resolve and deal damage to the unit at its new location, ultimately killing it.

Sequence:

• Icathian Rain is cast, placing six damage triggers on the chain
• The triggers resolve one at a time
• When enough damage accumulates to be lethal, Zhonya's Hourglass activates
• Zhonya's prevents the death, heals the unit, and recalls it to base
• The remaining damage triggers continue to resolve, hitting the unit at base
• The unit dies from the remaining damage

Nuances:

• This interaction works because Icathian Rain's triggers are reflexive and don't specify "at a battlefield", allowing them to hit the unit even after it moves to base
• The triggers cannot be countered individually by cards like Defy because they are triggers, not spells (though the original Rain spell can be countered normally)
• Zhonya's explicitly heals the unit when it activates (this is an errata)