How to make cast on striking?

How to make cast on striking?

Is there any way to make an item have a chance to cast a a spell on striking? I.E. I want to make a hero have a chance to cast Doom on what he is attacking when he is holding a specefic item.

Very ezy to do just take the orb of lightning(new) skill(under the special items folder) change the spell that it casts(default is purge), the % of casting it. Then just add the skill to what ever item you want it on.