M'kau's Mark is the scar-like disease that festers upon a person and opens a door to M'kau's influence and can turn the victim of the mark into a Minion. If the person does not become a Minion, the mark will become a festering, growing disease that will change the appearance of someone. It would spread over the body and overtake the top layer of skin, actually speeding up aging. It would not change the lifespan of the person but they will age quicker.