Back from the Dead: Doggett gets killed by the corrupt sheriff and evil townsfolk to keep the soul eater. The soul eater then digs him up and consumes it's death to kill itself saving Doggett.
Liquid Assets: The soul eater can consume conditions to cure them from people in exchange for being afflicted with them itself. This includes going as far as to cure death in exchange for dying itself.
Mercy Kill: What Mulder tried to do to the soul eater seeing it's immense pain. Ultimately, the creature killed itself by taking away Doggett's death and freed itself from the evil townsfolk.
Tragic Monster: The soul eater is a grotesque but very pitiable figure. It has the ability to eat the unhealthy organ of any human and cure it. However, it consumes the disease itself and is in constant pain.