Mages that play with life and death, that can bring the dead back to a half life state and command them... these magics are absolutely forbidden. And thankfully, rare to the point of being mostly theoretical.
Of course there are STORIES from the time of The Fall and onwards about wizards, witches, and even warlocks that were able to raise up their enemies to fight at their command, but the facts of these events are hazy at best.
In controlled settings it has been shown that magica can be a re-animating agent for muscle fibers and even minds, but it has mostly only created semi-worthless husks.
The one major event that firmly locked down the rule forbidden all death magics was the self perpetuating undead rat plague.
Somehow someone created a rat that could kill other rats, who in turn would rise and then attack and kill other rats, who would also rise. They would also attack any living thing they came across.
Thank the God they were "only" rats, and that they half life they spread did not cross over to humans.
But still... absolute condemnation for any who would play with such magics.
-Council of the Edges, annual review of fringe laws and enforcement