Passive Unit Creation Spell

Passive Unit Creation Spell

I want a spell that gives a (%) chance to create a unit when the hero attacks. Is this possible to do?

Events
A unit is attack
Conditions
Random integer between 1 and 100 is less than or equal to (X x (Level of (Ability) for (Attacking unit)))
Actions
Create (Unit) for (Owner of (Attacking Unit)) facing (Deafult Building Degrees)

thanks.