On September 1 2000, after the Phantom Troupe kill all the people at the Mafia's underground auction, Leech and the other Shadow Beasts are sent by the Ten Dons to deal with them. He, Porcupine, Rabid Dog and Worm engage in battle with Uvogin of the Troupe in the Gordeau Desert first. Shortly after they start, Uvogin blows Worm to pieces with his Big Bang Impact and reveals his spider tatoo. Undaunted, Leech, Porcupine and Rabid Dog charge at him together. Uvogin's right arm is immediately pierced and rendered useless by Porcupine's sharp quills. Taking advantage of that, Rabid Dog tears some pieces of flesh off Uvogin using his fangs and injects a neurotoxin that paralyzes Uvogin from the neck down. He wants to make Uvogin feel the pain they are going to inflict upon him. Thinking that Uvogin has become powerless, Leech approaches and transmits his special leeches to Uvogin. However, when he is boasting about how dangerous they are, Uvogin bites off a large part of his head, killing him.
Leech can control a great number of leeches which live inside his body. Some of them can be used for medicinal purposes while others carry contagious diseases. The special leeches he transmits to Uvogin will lay their eggs in the bladders of the victim and die within 24 hours. After hatching out, the baby leeches will cause them extreme agony when they urinate. Most victims will die of the sheer pain. However, the eggs can be expelled from the body safely by drinking a lot of beer.