How to make an auto-firing arrow?

[TreeTree]

How do I add to my hero so that when he gets hit, there's a chance an arrow might fly out of him and kill the attacking unit? I'm trying to make this completely out of the hero's control. So when this happens it won't change the hero's orders or anything like that. It's like the weapons in the battleship maps where they fire by themselves. I know how to do a random number, it's just the arrow part I can't figure out.

I'm hoping to have this as a passive skill so you can see it in the UI. I tried basing a skill off Thorns Aura but then I realized it's only for melee and it's 100% chance.

 

[NeuroToxin]

The weapons in battleship are based off of Phoenix Fire (I think) Which is a skill which fires randomly at enemies in range dealing a set damage.

 

[TreeTree]

Oo that worked perfectly! For anyone interested I'm recreating the arrow scene from 300 except it's 100 archers vs Leonidas.

By the way is there any way to edit trigger names? And what's the difference between an ability being hero or not?

 

[0WN3D]

Trigger name could be change..... Jus click on it to highlight it in blue.... Then click on it again.....

The difference from hero and normal ability is that hero ability can be learnt.....

 

[NeuroToxin]

A hero ability has multiple levels that can be learned only by heroes, and only heroes have access to these abilities, unit ability is something that a unit has, that CAN have multiple levels, heroes can have them, but they cant be leveled up with any unit, unless you research, or trigger.