I found a bug, don't know if you noticed already, but if you order him to cast it and the unit targeted runs away then he will follow until enemy is in range again and cast again, but then the beam effect will go to the wrong side(Instead of to the unit targeted it will show to the side where the unit stood when the spell was ordered).
Fix:
Create new global variable "LocLoc"
Then change the trigger "Blast Start" to this:
Blast Start
Events
Unit - A unit Starts the effect of an ability
Conditions
(Ability being cast) Equal to Blast
Actions
Custom script: local location udg_locloc
Sound - Play MarkOfChaos <gen> at 100.00% volume, located at (Target point of ability being cast) with Z offset 0.00
Sound - Play MarkOfChaos <gen> at 100.00% volume, located at (Position of (Triggering unit)) with Z offset 0.00
If (All Conditions are True) then do (Then Actions) else do (Else Actions)
If - Conditions
(Target unit of ability being cast) Not equal to No unit
Then - Actions
Set locloc = (Position of (Target unit of ability being cast))
Unit - Create 1 Blast for (Triggering player) at ((Position of (Triggering unit)) offset by 75.00 towards (Facing of (Triggering unit)) degrees) facing locloc
Custom script: call RemoveLocation(udg_locloc)
Custom script: set udg_LocLoc = null
Else - Actions
Unit - Create 1 Blast for (Triggering player) at ((Position of (Triggering unit)) offset by 75.00 towards (Facing of (Triggering unit)) degrees) facing (Target point of ability being cast)
Or no, didn't see it's based of shockwave and so ground AND unit targetable, I'll fix the tirgger above in a minute^^
Edit: Fixed it! Should work now.