Does Ezreal's leader ability trigger if you target 2 units with one spell (like Singularity)?

Ruling: Yes, Ezreal's leader ability triggers when you target two units with one spell like Singularity, because you are choosing 2 targets.

Nuances:

• The ability does not trigger with spells that affect "all units" where you don't actively pick/choose the targets
• The ability can still trigger if you select more than two targets (e.g., using a single target spell modified by Singularity)