Bizarre Human Biology

Maybe the character was born a Mutant, or belong to a Human Subspecies, or have gone far enough up the Evolutionary Levels as part of the goal of evolution, or underwent extensive Bio Augmentation of the essentially permanent kind... Or perhaps they were even created as an Artificial Human from the get-go. The bottom line is, this human character's biology, while not technically alien, cannot be considered "normal human" by any stretch of the term, be it due to having extra organs (duplicate or not), wildly different biochemistry, abnormal nutritional requirements, or even possessing completely new cellular organelles.

The trope can come into two flavours:
 * Standard: These are fictitious in principle, and thus typically the domain of Speculative Fiction.
 * Truth in Television: some of the detailed aspects of our biology can be downright bizarre to us, even if they technically make sense. Additionally, there are real-life medical conditions that technically result in abnormalities to an otherwise healthy human biology (see Real Life section).

Note that not all cases of Human Subspecies, Transhumanism, Mutants, Bio Augmentation, etc. lead to Bizarre Human Biology. They are only possible ways for attaining this trope.

Compare and contrast Bizarre Alien Biology, which may overlap with this trope in cases of Half Human Hybrids or Panspermia.

Anime And Manga

 * Italy's Idiot Hair in Axis Powers Hetalia is shown in the comic to be an "erogenous zone". It's unclear if the note was referring to his scalp reacting to the hair being pulled, or if he has actual feeling in the hair, but the fandom tends to run with the latter, and usually applies the same principle to the other curl-bearing nations. On a creepier note, at least one fic goes to the logical extreme of the hairs being sensitive and has one bleed when severed. Also, Norway's curl actually floats around, detached from his head.

Comic Books

 * The Ultimate Marvel version of Mr. Fantastic's body is an infinitely extensible fluid-filled sack containing, in place of an alimentary canal and other organs, just a squishable bolus of microbes that perform all metabolic functions. Yes, we know; Artistic License Biology. Chalk it up to Rule of Cool and leave it at that.
 * Plastic Man is literally inorganic after his Origin Story; this actually makes him immune to Brainwashing, since his brain itself is apparently plastic.
 * Post-Extremis, it was revealed that Tony Stark had managed to change how his insides were organized.

Fan Works

 * While Rei Ayanami is canonically known to be at least partially human, the specifics aren't made clear. To compensate, Fanfics tend to depict her with either this trope, Bizarre Alien Biology, or both, each in various ways. To list them all would be a herculean task, given the size of the fandom; one notably common issue, however, is whether or not she has an S2 Engine/Organ, and its exact role in her physiology.

Films

 * Star Wars: Humans, as well as all other living species in The Verse, possess "midi-chlorians," mysterious organelles which have some intricate connection to the Force.

Literature

 * Human soldiers from Old Man's War have green photosyntesizing skin, cat eyes and nano-bots instead of blood.
 * The Eighth Doctor Adventures novel The Blue Angel features an Alternate Reality Episode in which the Doctor is theoretically human. He has two hearts, no navel, and an unusual aversion to the cold. It's probably related to the fact that his mother is a mermaid.

Live-action TV

 * The Sebeceans in Farscape are  They have improved physical strength and eyesight (humans are apparently practically blind by the standards of other races) but fewer redundant organs and an extreme (seriously) weakness to high temperatures.

Music

 * Vermillion Lies have a song entitled "Long Red Hair", about a pair of Conjoined Twins born joined at the hair.

Tabletop Games

 * Warhammer 40,000's Adeptus Astartes.

Video Games

 * In Parasite Eve, the protagonist Aya possesses a more benign/passive form of the "evolved" strain of mitochondria serving as the franchise' Big Bad, which are not only a self-aware Hive Mind that can hijack their "hosts" and act like The Virus, they possess actual superpowers, which include Spontaneous Combustion and Body Horror transformations!

Anime

 * Souther (or however you want to Romanticize it) in Fist of the North Star has situs invertus totalis (see Real Life section below) - which means that Kenshiro's first attempt to defeat him fails utterly. You see, when the organs invert, so do the pressure points Hokuto Shinken relies on...

Literature

 * In the mystery story "The Image in the Mirror" by Dorothy L. Sayers, a key plot point is that one of the characters has situs inversus.

Video Games

 * Metal Gear Solid 2: Fortune was born with her heart on the right side, due to situs inversus (see Real Life section).

Real Life
"Tony Danza Claus: I really wanna teach a troll sex ed class. But stick to actual facts. "The blood rushes into the penis, which is basically an elongated clitoris made of the same erectile tissue of the labia. Then the man puts his re-purposed clitoris into the vagina, which is lubricated by mucus, just like snot, and after so long the man ejaculates, which means a funny smelling liquid called semen, which comes from a gland in his asshole, mixes with some worm-like creatures and then comes out of where he pees. "So sex is basically snot and blood and rear end gravy and worms all thrown into a big sweaty bowl that can result in a baby, which cost on average $28,000 a year. Any questions?""
 * Situs inversus, especially the totalis version, is a congenital human condition where the internal organs are in reverse of where they normally are (heart with apex on the right, liver on the left, etc.). Absent any actual congenital defects, such individuals can lead otherwise perfectly normal lives.
 * There are also quite a few other congenital birth disorders, from mostly harmless (hare lip, extra finger(s) or toe(s)), debilitating (limb deformities), and probably not going to survive for long after birth, if the infant even lasts that long (born without most of the brain).
 * Of course Situs Inversus Totalis can still pose problems once other medical issues arise. For example: a patient pointing to the opposite side of where the organs normally are, which can delay proper diagnosis (which could fatally delay proper treatment). As such, it is considered advisable for people that know they have Situs Inversus to wear an ID tag (in case that person should fall unconscious or otherwise be rendered in a state that prevents them from mentioning their complication).
 * About 1/400 people has their kidneys fused into a horseshoe-shape, which is mostly asymptomatic. Mel Gibson is one notable carrier.
 * HeLa is an immortal, single-celled organism with 82 chromosomes. It's a culture of cancers cells drawn from a patient in the 1950s, which has continued to undergo cell division and grow, bizarrely unaffected by the Hayflick Limit, and at this point the number of such cells grown has easily surpassed the number of cells in the original donor's body.
 * An... interesting and technically correct description of intercourse popped up in Something Awful (a middle-school teacher requested things to make her sex ed class memorable):


 * 7 Terrifying Things They Don't Tell You About Pregnancy
 * Does chimerism count? Genetic chimerism in humans came to light when two new mothers—one in Massachusetts, the other in Washington State—gave birth to children whose initial DNA tests showed that the women's husbands were the biological fathers, but that they were not the biological mothers. Further tests showed that both mothers had two different DNA profiles in different parts of their bodies.
 * Wisdom tooth extraction is an experience that is apparently universal to your average teenager or vicenarian. If they aren't getting them removed, then lucky them, they never grew them at all! And then there are those who never had them removed because they had so much room in their mouths that the wisdom teeth were able to grow in and settle in as happy and comfortably as any of the other teeth they grew. Some even have more than one set of wisdom teeth in there.