SC2Mapster

I doubt any triggers were used for the ability. The actor data is where you will find your answer. Looks like the actor uses "drag" on the effect. Not sure if sc2 has that.

I would advise looking into how Blizzard has made the Skeletal Mage ultimate for Xul in Heroes of the Storm. The most recent version of it summons units in an orientation that are rotated by dragging your mouse cursor before releasing. Since HotS is based on the same engine as SC2 it is possible the same mechanics can be used, assuming there have not been too many major diversions between the game engines.

If using such mechanics is possible, one would create a unit at the initial target and then rotate it to the drag vector, using triggers if required.