short answer YES
the reason of why we need to kill necromancer is because nicromancer COULD be the grave digger in disguise and now this may sound stupid BUT if nicromancer can bring back the dead then whose to say grave digger didnt self revive and become neromancer because after all we see THE grave digger present in the trials therefore grave digger decided to spawn back in so YES we need to kill necromancer before necoamcner becomes too strong AS grave digger
GRAVE DIGGER IS SPYING ON TDS USING THEIR NECROMANSER ALTER EGO
