There’s definitely a copy/paste issue there. I only ran one character with the PrC, but used Good Will, Poor Fort and Ref Saves. I also changed requirements from specializing in necromancy to having Spell Focus (Necromancy) since I don’t use specialists in Dark Sun. I kept the Spellcasting as is but added an additional ability at level 1.
Master of the Undead: Your class level is added to your caster level for purposes related to creating and controlling undead.
I also modified two secrets:
Necromantic Specialist: This ability reduces the level requirement necessary to create a specific type of undead through a casting of create undead or create greater undead by 1/2 your class level.
Undead Horde: You can control an additional 2 Hit Die worth of undead per caster level with any necromancy spell. You can take this ability multiple times, each time adding an additional 2 Hit Die worth of undead per caster level.