Another Custom triggered ability problem

All I want for the trigger part of the ability is for a crater to be made on the targeted area. I tried making a dummy unit so that I can move a region on it and make the crater but I cant make the dummy unit appear at the target. I need help please.

Xtil

ok, get the target unit

then with whatever event you trigger it from, you do this:

Action

Special Effect - Create Special Effect on a Unit.

Then On the dialog box, specify the target unit, change "overhead" to "origin" and choose the type of special effect you want.