If you use Falling Star on an enemy unit with 3 might or less as their only unit on the field, does the 2nd instance of Falling Star have to target your own unit after the first instance kills it?

Ruling: No, you select both targets when the reflexive triggers are finalized on the chain (before any damage is dealt). You can target the same unit twice, and if the first instance kills it, the second instance resolves on that same target dealing no damage.

Sequence:

• Cast Falling Star (no targets chosen yet)
• Falling Star resolves, putting 2 reflexive triggers on the chain
• Both reflexive triggers are finalized on the chain and targets must be chosen at this time
• First reflexive trigger resolves, dealing 3 damage
• Second reflexive trigger resolves, dealing 3 damage to the same target

Nuances:

• Targets cannot be changed once chosen during finalization
• If the target leaves the board (via Retreat, etc.) after targets are chosen, the spell resolves as NULL with no damage dealt - there is no fizzle or retargeting
• This can bypass Zhonya's: the first damage triggers Zhonya's replacement effect, then the second damage still resolves on the same target and can kill it
• If the first instance kills a unit with Deathknell, that Deathknell trigger resolves before the second Falling Star instance, potentially saving the second target
• If a unit is removed via Retreat before Falling Star resolves (reacting to the initial cast), then when Falling Star resolves and you must choose targets, you must target available units (potentially your own)