Ok... your spells seems pretty confusing since I can't get what you really want. I'll just ask you: Do you want ALL the heroes on the map? If you want in a specific range I will change the condition in red. Now, let's see.
Create a spell let's say based on Thunder Clap. Give it NO damage, NO duration, NO buff, change icons, change mana cost, change cooldown, give one level. ^_^
Now, let's go to the dummy unit. Create one dummy unit (read FAQ to find out how) and give it an ability with a singular target that does only damage (umm... I'll think about a good one) and give it monsoon Target art. Hehe, give the dummy unit that ability.
Now, let's go to triggers. Create an Unit Group variable and assign it array with 16 values.
Event - An unit starts the effect of an ability
Conditions - Ability being cast equal to (Yourability)
Actions - Pick up every unit within (Playable Map) matching Conditions ((Matching Unit) is A Hero) equal to true and ((Matching Unit) belongs to an enemy of (Owner of (Casting Unit))) equal to true and do actions
->Create 1 (dummy unit) at position of (Picked Unit)
->Order (Last Created Unit) to [Whatever skill you pick] (Picked Unit)
->Add (Picked Unit) to Unit_Group[(Player Number of (Triggering Player))]
Wait 0.10 seconds
Pick Up every unit in Unit_Group[(Player Number of (Triggering Player))] and do Remove (Picked Unit) from the game.
That's all you need!