Dummy triggers noob

[Impereal Gardian]

Ok, so im trying out just now on how to do dummy units. so far, I understand it except one small trigger detail.

for example:
"Order last created unit to <silence> target unit of ability being cast"

How do i order a dummy unit to cast silence instead of the basic spells that are there?

EDIT: I dont remember how to post the trigger thing, but here is a picture of my trigger if it helps any. (the problem is the stuff like mass teleport, there isnt a way to customize it so far as i know) http://prntscr.com/2ahz76

OHHHHHHHHHHHH SORRY! I just realized this is the requests page :L

 

[Impereal Gardian]

Is there a way to take this post down?