If Fiora gains Mighty (and thus Deflect) after I've already paid for and finalized a spell targeting her, do I have to pay for Deflect? What about with Falling Star's reflexive triggers if the opponent reacts with Call to Glory?

Ruling: Once a spell or ability has chosen a unit as its target and been finalized to the chain, you do not have to pay for Deflect if the unit gains the keyword afterward.

Sequence:

• If Falling Star resolves first, then its reflexive triggers pick targets and finalize afterward - if Fiora gains Deflect before those triggers finalize, you must pay for Deflect
• If the opponent reacts to Falling Star (before it resolves) to give Fiora Deflect, then when Falling Star's reflexive triggers are created and pick targets, you will have to pay for Deflect
• If the opponent waits until after Falling Star resolves to give Fiora Deflect, the reflexive triggers have already finalized their targets, so you don't have to pay

Nuances:

• You can decline to pay costs incurred by triggered abilities when finalizing them, causing the trigger to be retracted and never go on the chain
• This means you cannot be forced to recycle runes to pay for Deflect on triggered abilities
• You can choose to decline Falling Star triggers if Fiora with Deflect is the only legal target, or if you don't want to kill other units for any reason