Early in their training, Dark Mages advance faster than magicians of other specialties, but once they reach the Magus Realm, their progress often stalls due to advancement difficulties.
However, the Dark Magic World has two forbidden training methods, one of which is becoming a Necromancer.
A Necromancer is a Dark Sorcerer who, through a special method, entirely sacrifices his body in exchange for powerful dark magic power. Although their physical form ceases to exist, their soul continues indefinitely. Not only does this greatly increase their magic power, but it also makes them impervious to any physical attack.
However, the Necromancer's training method is exceedingly arduous, with success rare, and most of the dark sorcerers who choose Necromancer training often lose their bodies and souls.