Target is: 1-3 Creatures or Conjurations
Not 3 Creatures or Conjurations
Card text:
You may make this attack against up to 3 different targets in the same zone. Damage from this attack is critical (ignores armor). Roll for each attack separately.
As far as I can tell, these are 3 separate attacks that you target 3 times one for each missile.
You got it wrong. It allow you make this attack on 1, 2 or 3 targets, not "You may make 3 times this attack [...]".
While we are at it... since this is not a zone attack, +Ranged works on it... but does it only apply to the first target only or the three targets?