How does Icathian Rain work - do you choose targets when you cast it or when it resolves?

Ruling: Icathian Rain uses a reflexive trigger (indicated by "do this:" text). You choose targets when it resolves, not when you cast it. When it resolves, it creates 6 separate triggered abilities on the chain, each dealing 2 damage to a targeted unit.

Sequence:

• Play Icathian Rain
• Players can react
• Icathian Rain resolves, putting 6 reflexive triggers on the chain
• Choose targets for the 6 reflexive triggers
• Pay additional costs for each trigger targeting an enemy unit with deflect
• Players can react between each trigger
• Each trigger resolves separately, dealing 2 damage

Nuances:

• Any card with "do this:" text creates a reflexive trigger that goes on the chain upon resolution
• This applies to other cards like Falling Star and Twisted Fate's attack ability
• The design creates more opportunities for counterplay - opponents can respond between each damage instance, and deflect costs apply to each trigger separately
• If ability-countering cards are released, having separate triggers makes the spell less vulnerable to being fully countered