Counterattack
Such an evil undead like the ghoul had never appeared on the knights' plane.
Some wild undead beings occasionally appeared in rural areas. However, most of those were low-level skeletons with creaking bones, or withered corpses that shambled about slowly. The worst of those were only spectres that had lost their souls.
As for an elite undead such as ghouls- they never appeared naturally without the existence of an undead manipulator.
Today, under the infection of the plagues and viruses of the voodoo beasts, along with the catalyzation of the black fog, the injured witcher-knights were unable to resist the powerful magic and were all converted into strong and lithe ghouls. Perhaps because the physiques of this group of knights were extremely exceptional, the ghouls that they turned into also possessed extraordinary strength and physique.
Of course, the agility unique to ghouls was once again amplified as well!