Does Falling Star have to pay Deflect twice on a unit with Deflect?

Yes, you must pay the Deflect cost twice if both instances of damage from Falling Star target the same unit with Deflect.

According to Rule 809.1.c, the Deflect keyword acts as an additional cost for spells and abilities an opponent controls "for each time they choose me." Because Falling Star has two separate instances of "Deal 3 to a unit," it technically chooses (targets) a unit twice if you decide to select the same unit for both instances.

Key Details:

• Per-Targeting Cost: Deflect is not a one-time cost per spell; it is a mandatory additional cost for every individual instance of targeting.
• Additional Costs: These costs are mandatory and must be paid when you play the card (during the "Pay Costs" step of the chain finalization). If you cannot pay the required amount (e.g., if the unit has Deflect 2, you must pay 2 Power for each targeting instance, totaling 4 Power in Deflect costs), you cannot legally target that unit with both instances.

This interaction is confirmed by multiple RiftJudge FAQs (such as FAQ #5107 and #8782), which clarify that for multi-target spells like Falling Star, the Deflect cost applies to each specific time the unit is chosen.