Return of King Arthur - Creature Design

This is a Design Process Principle project, the story for this concept is a fantasized version of the black death plague that happened in the 14th century in which the disease evolved into a deadly virus that caused the infected people to turn into deadly creatures that hunt for people. These foul creatures are agile, powerful and cruel, but are constantly enduring the pain brought to them by the sickness, the only way to set them free from the pain is to end their miserable bloodfest.