When can Windwall be used to counter cards with reflexive triggers like Icathian Rain and Falling Star - only on the initial cast before reflexive triggers are declared, or can you wait to see the targets and then counter the reflexive triggers?

Ruling: Windwall can only counter the initial spell before it resolves. Once the reflexive triggers are on the chain, the initial spell has already resolved and cannot be countered anymore. The reflexive triggers themselves cannot be countered by Windwall because they are not spells.

Sequence:

• Windwall must be used on the initial cast of the spell
• Once the spell resolves, reflexive triggers go on the chain
• At this point, the initial spell can no longer be countered
• The reflexive triggers cannot be targeted by Windwall as they are not spells