Can a player play a reaction (Retreat) that was drawn from Hidden Blade's resolution to save another unit targeted by the same Falling Star that triggered Hidden Blade?

Ruling: Yes, after Hidden Blade resolves (killing the unit and drawing 2 cards), players can add new reactions to the chain before Falling Star continues resolving its other targets.

Sequence:

• Falling Star is played targeting two units (one at battlefield, one at base)
• Hidden Blade is activated in response, targeting the battlefield unit
• Hidden Blade resolves: kills the unit and draws 2 cards
• Players can now add reactions to the chain
• Retreat (drawn from Hidden Blade) can be played targeting the base unit
• Retreat resolves, saving the base unit
• Falling Star continues resolution

Nuances:

• The Retreat targets a different unit than the one killed by Hidden Blade (it saves the base unit, not the battlefield unit that was already killed)