When using Retreat to counter Icathian Rain, can I wait until after damage targets are assigned, or must I counter before targets are chosen?

Ruling: You can counter Icathian Rain at multiple points - either before targets are chosen (when Rain first goes on the chain) or after targets are assigned (once the 6 triggered abilities are created). The optimal timing depends on your strategic goal.

Sequence:

• Rain goes onto the chain with no targets
• Reaction window (can counter here before targets chosen)
• Rain resolves and creates 6 distinct triggered abilities on the chain, each with their own target
• Reaction window (can counter here after targets chosen)
• Each rain trigger resolves one at a time, each followed by a reaction window

Nuances:

• If you counter before targets are chosen and only your unit is on the field while your opponent has a unit, your opponent is forced to target their own unit
• If you counter after targets are chosen, your opponent may have already committed damage to specific targets
• All 6 rain triggers must choose valid targets even if it means targeting the caster's own units (triggers cannot be denied unless there is a deflect cost)
• Most other spells (like Falling Comet) choose targets when the spell goes onto the chain, so there is no opportunity to react before target selection - Rain is unique due to its "Do this" reflexive trigger structure