Read FAQ please. It should help you for some stuff. Usually dummies are very small, without model, non consumers of food, non-hero and non-workers, with Locust and other abilities needed to be cast depending on the spell. Now, you go for triggers if you want triggable.
Ok, depending on the skill you want to give (Thunder Clap or War Stomp), give the Dummy one skill which would do the appropriate effect. If you would want your Thunder Clap to do 400 damage then make sure that the dummy's Thunder Clap DOES 400 damage.
Event - A unit Starts the Effect of An ability
Conditions - (Ability being Cast) Equal to (Your ability)
Actions - Create 1 Dummy [Note: This is actually your dummy unit] for owner of (Casting Unit) at position of Target Point of Ability being cast
- Set "Dummy_AOE" [Your unit variable] = (Last Created Unit)
- Order Dummy_AOE to ... [note: Whatever skill you gave to te dummy.).
- Wait 0.10 seconds
- Remove Dummy_AOE
That should do it.