If I cast Falling Star and choose 2 units, then my opponent plays Retreat on one of them, do I need to do 3 damage to my own unit instead?

Ruling: The timing of when Retreat is cast determines what happens. Falling Star does not select targets when cast - it selects targets when it resolves by creating two reflexive triggers that each choose a target.

Sequence:

• Falling Star is cast and added to the chain (no targets selected yet)
• Opponent has an action window to react
• Falling Star resolves and creates two reflexive triggers on the chain
• Each reflexive trigger individually selects a target (can select the same target twice)
• Once targets are selected, they are locked in and cannot be changed

Nuances:

• If Retreat is cast BEFORE Falling Star resolves (before targets are selected): You must select from remaining legal targets. If only one enemy unit remains, you can target it twice. If no enemy units remain and you have units, you must target your own units.
• If Retreat is cast AFTER Falling Star resolves (after targets are already selected): The retreated unit's trigger simply whiffs and does no damage. You do NOT reselect targets or redirect damage to other units.