Virgil Incanto was a serial killer with an unusual genetic condition. He was lacking the enzymes needed to produce several essential fatty acids. In order to survive, he would regurgitate a lipase containing slime that would break down the fat in his victim's flesh allowing him to consume the free fatty acids before the rest of the body dissolved. Mulder and Scully were called in to investigate the killings because of the bizarre slimy nature of the corpses.
Incanto chose his victims in internet chat rooms where larger women would go, using the alias 2Shy. Since they had more fat on their bodies than average, they were the perfect choice to keep him alive. He was shot by one of his victims after he attempted to eat Scully. He survived the shooting but was in bad shape during his interrogation with Scully concerning the cases of 47 missing women. He was proud of the fact that they were all his victims and he showed no remorse for what he did to keep himself alive. He died in prison from his condition after showing severe skin problems due to the lack of oil and fat in his diet. (TXF: "2Shy")