Does Volibear's Imposing ability trigger when an opponent moves units into a battlefield, and if so, how many cards are drawn when multiple units move at once?

Ruling: Volibear's Imposing ability does not trigger when Volibear is already on the base and an opponent moves a unit into that battlefield. When multiple units move simultaneously to a battlefield, the ability triggers once and draws 1 card.

Nuances:

• The ability only triggers based on the action of moving units, not the number of units moved in a single action