These strange aberrations are after your mind, your psionic energy, and more importantly the total domination of your kind. Learn the history of the Mind Flayer.
One of the most fearsome creatures to ever adorn the cover of multiple Monster Manuals. These paranoid spheres of pure evil are working on their plans of world domination, just as soon as they kill every other imperfect Beholder in existence.
You lived a really evil life, so why should the afterlife be any different. Becoming a Wraith isn’t for the faint of heart, and neither is trying to fight them.