looking for an ability

What I'm doing is making a spell that will act like a bow attack, but damage will be figured out by triggers.

I just need a spell that will allow it to shot like a bow and i need to be able to detect each attack.

Maybe you could use searing shot or poison shot or etc...?

You can use Poison Arrows (or slow,black) and check for buff.

If the hero is melee i'd suggest Acid Bomb, it has moddable projectiles and you can remove all of its effects, making it a very good dummy abilty for this sort of thing.