Mighty Shrubby!
Xukong had been terribly worried upon seeing the state of Lin Mu. He didn't know what kind of damage had been caused by the tribulation lightning either. The thing was that Lin Mu was hit by was pure tribulation lightning, but it was not intended for him.
If it was punishment tribulation lightning, Xukong would be able to assess it much better. But this was something that he had rarely seen happen before. He had heard of certain cultivators who had special cultivation techniques that needed the Tribulation lightning to progress.
But even they didn't use pure tribulation lightning that was intended for someone else. The laws of heaven simply did not work like this. The tribulation lightning that was intended for someone would only hit that specific person.