I think they uses dummy units with starfall
[trigger=Starfall]Starfall
Events
Unit - Unit start casting a ability
Conditions
Casting ability is ??? equal to true.
Actions
Set SFCaster = Casting unit
Set SFCasterLoc = Location of SFCaster
Set SFDummySpawn = Location of SFCaster
Unit - Spawn 1 SFDummy for owner of SFCaster at SFCasterLoc
Unt - Issue Last Created Unit to Night Elf Priestess of the moon - Starfall
Unit - Add 2 second Generic expiration timer to last created unit[/trigger]
This is just tutorial. And please continue yourself