When playing Icathian Rain, do you choose all damage targets before your opponent can react, or can you choose targets one at a time between reactions?

Ruling: You cast Icathian Rain without declaring targets initially. After opponents can react, the spell resolves by creating 6 triggers that are added to the chain. You declare the target for each individual trigger when those triggers are finalized, and opponents can react between each trigger resolving.

Sequence:

• Cast Icathian Rain (declare no targets)
• Reactions can be made
• Icathian Rain begins resolving, 6 triggers are added to the chain as pending
• Icathian Rain finishes resolving, 6 triggers are finalized and targets for each individual trigger are declared here
• Reactions can be made
• Last trigger resolves
• Reactions can be made
• Continue for each remaining trigger

Nuances:

• Deflect costs would be paid when targets are declared (when triggers are finalized)
• Opponents can react after each individual trigger resolves