If Singularity targets two opponent units and one is Retreated in response, do you have to retarget Singularity or does it still deal damage to the remaining unit?

Ruling: You cannot retarget Singularity once targets are chosen. The remaining legal target will be dealt 6 damage, while the illegal target (the Retreated unit) causes that part of the spell to resolve to no effect.

Sequence:

• Targets are chosen when Singularity is added to the chain
• If a target becomes illegal (e.g., via Retreat) before resolution, that portion resolves to no effect
• Any remaining legal targets are still dealt 6 damage

Nuances:

• This differs from Falling Star, which uses "do this" text creating two separate reflexive triggers that choose targets at resolution time, allowing responses between each instance
• Singularity targets "up to 2 units" so 0 targets is allowed if both become illegal