The following is a comprehensive list of all mutants in The House of the Dead: Overkill and its Extended Cut expansion. Serving as the main enemies, mutants are residents of Bayou City who have been infected by Formula X.
- Commoners: Once innocent townsfolk. They have a pretty variable appearance. Examples:
1. A mutant in a blue polo shirt.
2. A mutant in a red plaid polo shirt.
3. A mutant in a green polo shirt.
4. A mutant mutant in a lavender t-shirt.
5. A mutant in an orange plaid and blue flannel-lined jeans
- Doctors: Mutated medical doctors.
- Nurses: Mutated nurses. They prefer hypodermic needles to any other weapon.
- Surgeons: Mutants in surgery attire.
- Patients: Mutated hospital patients.
- Clowns: Mutated clowns. They can also throw knives in the boss battle with Nigel and Sebastian.
- Ride Operators: Mutated amusement park workers.
- Hobos: Mutated old homeless people.
- Football Players: Mutated members of The Bayou City Roosters football team. Interestingly enough, all of them are fat.
- Prison Inmates: Mutated criminals in orange prison clothes who appear in the jailhouse and on the train.
- Cops: Mutated Bayou City police officers. Some of them use riot shields to block gunfire and riot helmets, which make it harder to kill them with headshots. They also share models with mutated prison guards. In the Extended Cut, their models are also used in the slaughterhouse for mutated guards, with the only difference being caps on their heads.
- Business Suit Mutants: While it's unclear who they are exactly, judging by their appearance and id badges on their suits, it can be assumed that they are mutated government agents/researchers/other important figures.
- Rage Mutants: Strong and fast Mutants. In the Extended Cut version, they can be defeated only during a QTE sequence. In the Wii version, they must be shot or pushed back, before they will bite G and Isaac. Wrestling with them is only avoidable in the Wii version. They have a barcode tattooed on a pectoral and orange pants, meaning they were inmates or test subjects of Formula X. In Extended Cut they also have some design differences, while in the Wii version they appear to have some hair left, in Extended Cut they are completely bald.
- Pukers: Mutants with bloated bellies that puke acid or explode. Do not shoot if they are close in the Wii version, you will be given a chance to wrestle with them. These mutants are filled with pus, acid, and blood. They can also accidentally harm other mutants. They also have a black version, which is spawned by The Mother.
- Spawnlings: (Extended Cut only) Mutant babies who can crawl on the walls and attack by leaping head-on.
- Strippers: (Extended Cut only) Mutated strippers that appear in the Pink Pussycat.
- Bikers: (Extended Cut only) Mutated members of the biker gang who hang out at Mort's Saloon. They wear t-shirts with an image of a skull with a spade on the forehead.
- Slaughterhouse Workers: (Extended Cut only) Mutated butchers. They carry cleavers or knives.
- Flayed Mutants: (Extended Cut only) Mutants that appear in the slaughterhouse without skin, revealing their muscles and intestines.
- Actors: (Extended Cut only) Mutants dressed in green zombie masks and skeleton suits, appearing only during the spooky house ride in the amusement park. They are not hostile, but can be killed for points and the violence meter. They are always gibbed when killed.