User blog comment:Naruto12354/Has anyone else done this?/@comment-5469467-20130128044713

I don't know about what you're encountering, but I do recall that there is a glitch that can cause Mehrunes Dagon to glitch out when you use the Wabbajack on him. Here's some stuff from his page:
 * - During the last part of the main quest, when Dagon enters the area, equip the Wabbajack and blast him with it. This will change his stats to a random enemy's stats, thus making him mortal. Sometimes it may kill him.
 * - Wabbajack has also been known to cause him to melt into a big red blob.