Can Not So Fast stop multi-target spells like Singularity, or only single-target spells?

Ruling: Not So Fast can stop multi-target spells like Singularity. However, it works differently against spells with reflexive triggers ("do this:") that create multiple separate effects.

Nuances:

• Not So Fast can counter the entire Singularity spell (which targets 2 units as one spell)
• Not So Fast cannot counter the entire Falling Star or Icathian Rain spells because these create multiple separate items (2 and 6 respectively) via reflexive triggers - it can only counter one of those individual items
• Not So Fast can counter abilities (like Yasuo and Volibear abilities), unlike some other counter spells
• Not So Fast is not useful for spells that don't target your units