Can I target another unit with Singularity if one of the 2 targets I chose gets Retreated in response?

Ruling: No, you cannot retarget. Targets must be locked in when you put the spell on the chain, and if someone responds with Retreat, you cannot change your targets.

Sequence:

• Declare targets when putting Singularity on the chain
• Targets are locked at that point
• If opponent responds with Retreat on one target, the original targets remain unchanged