One day, Leprosy was partaking in alchemy when one of the chemicals he produced caused his blister-ridden face to excrete a red, viscous liquid. He preserved this liquid, which had now taken on the texture of slime, and removed a small portion to freeze. After it was frozen, he noticed that it was in fact pure leprosy concentrate, and had hardened into a solid material that was very porous. After experiencing the immense power the Jaundice Pendant had brought him in the Spicy Skittle Cereal review, he was eager to create a stone capable of this immense power himself. He was delighted to find out that the stone did indeed have the power to inflict leprosy on others, as well as to boost his power and stamina by an immense amount. He now guards the Leprosy Stone from others, hoping to keep the immense power to himself.
The creation of the Leprosy Stone caused the original red Phlegmstone, the Measles Stone, to instantly disintegrate. The dust of the Measles Stone caused a measles outbreak in Washington in early 2019.
The Leprosy Stone, most notably, has the power to inflict leprosy upon another person at the wearer's use. This leprosy is immensely powerful, often results in temporary loss of limbs, and causes red, chicken-pox like blisters to break out on the target. It also boosts the wearer's power by a large amount, allowing them to become very strong, have high stamina and become very durable. However, it causes the wearer to become more primitive in nature, often weakening speech capabilities and fine motor skills to a large degree. It also causes the wearer's leprotic blisters to worsen, but this is temporary.