Does Vanguard Helm activate to buff another unit when the first unit is killed by Singularity?

Ruling: No, Vanguard Helm does not activate when a unit is killed by Singularity because Singularity is a single item on the stack, so both units die at the same time.

Nuances:

• This interaction would be different with Falling Star or Icathian Rain, where the helm would trigger because each instance of damage is its own effect on the stack
• With multi-instance damage spells, the helm triggers and intercepts the stack during cleanup as damage goes from pending to finalized