Does casting Singularity (which targets two units) activate Ezreal's Legend ability that requires choosing enemy units/gear twice this turn?

Ruling: Yes, casting one Singularity does activate Ezreal's Legend ability. When you target two units with a single spell, you have chosen units twice, which satisfies Ezreal's requirement.

Nuances:

• This ruling is confirmed by developer commentary ("red text") but the comprehensive rules support is unclear or debated
• Each individual target chosen counts as a separate instance of choosing, even when done by a single spell
• The ability works whether you: (1) target one unit twice with different spells, (2) target two units with the same spell, or (3) target two units with different spells
• Deflect only adds power cost once per spell regardless of how many times that spell targets the unit with Deflect
• Damage is dealt simultaneously to multiple targets (per rule 404.1.d), but the choices of targets are still counted individually for Ezreal's purposes