If Player B plays Falling Star and Player A retreats their only unit, leaving only Player B's unit and a Pouting Poro (with deflect) on the battlefield, can Player B choose to target the deflect unit and decline to pay the deflect cost instead of being forced to damage their own unit?

Ruling: Yes, Player B can target the unit with deflect and decline to pay the deflect cost, causing the reflexive trigger to be removed from the chain instead of being forced to target their own unit.

Sequence:

• Player B plays Falling Star, paying its costs
• Player A plays Retreat, returning their unit to hand
• Falling Star resolves, creating two reflexive triggered abilities
• For each reflexive trigger, Player B must choose a target
• Player B can choose to target the unit with deflect
• When targeting the deflect unit, Player B can decline to pay the deflect cost
• If the deflect cost is declined, the pending trigger is removed from the chain
• This can be done for both reflexive triggers

Nuances:

• This only works because Falling Star creates reflexive triggered abilities (indicated by "do this:" wording), not direct spell effects
• For regular spells that target (not triggered abilities), deflect costs are mandatory and cannot be declined
• The deflect unit is always a legal target; the choice to pay or decline happens during cost payment, before legality is checked for resolution
• Even if other units are available as targets, Player B can still choose to target the deflect unit and decline to pay