How do Falling Star and Icathian Rain work with Retreat, specifically: Can they target your own units? What happens if there are no legal targets? Do they return to hand or fizzle?

Ruling: Falling Star and Icathian Rain do not specify "enemy units" so they can and may have to target your own units. Riftbound does not have fizzling. These spells can be played with 0 targets on the field because they do not directly target - they create reflexive triggers after resolving. The claim that these spells return to hand is false; they go to trash after resolving normally.

Sequence:

• The spell (Falling Star or Icathian Rain) is played and finalizes onto the chain
• The spell resolves and creates reflexive triggers
• The triggers attempt to finalize onto the chain with valid targets
• If an opponent retreats units in response to the spell (before triggers are created), the triggers must target remaining valid units (including your own if no enemy units remain)
• If an opponent retreats units after triggers finalize and target their units, the triggers resolve to 0 effect
• If no valid targets exist when triggers try to finalize, the triggers simply fail to finalize and are not added to the chain

Nuances:

• If an effect fails to finalize onto the chain for any reason (including no legal targets), the effect is removed from the chain and placed back into your hand if it is a card - but this applies to the finalization step before reactions can be made, not after
• Once a card successfully finalizes onto the chain, it proceeds with normal resolution and goes to trash (if it's a spell) - costs and targets cannot be undone at this point
• Falling Star and Icathian Rain themselves do not require targets to finalize, so they will go to trash even if no units exist on the field