Bizarre Alien Reproduction

"Wuffles: You are misinterpreting what you saw, Pieter! Pieter: I saw the tentacles! I know what that means! Wuffles: My reproductive organs are in my mouth! It doesn't work that way!"

- Nobody Dies

Okay, you've got your Humanoid Aliens. But no matter what you do, they don't seem alien-y enough. So you add some Bizarre Alien Biology. What's the easiest way to do this? Sex! Guaranteed to appeal to somebody, and if done right, it can look like something other than just just being a pervert or possibly Fan Service. It should be added that no matter how deviant it seems to us, Good People Have Good Sex and this counts as good sex, even if it is interspecies.

Sometimes related to G-Rated Sex. May fall into You Fail Biology Forever, if the reproductive method fails to generate enough offspring to maintain a population. Note for examples to not include anything related to cultural practices; we're limited to the biology of reproduction here. Put Non-Mammal Mammaries, Exotic Equipment, and Mister Seahorse on their own page, please. See also Face Full of Alien Wingwong.

Anime and Manga

 * The Twelve Kingdoms has a truly weird reproductive system involving marriage but apparently no sex: when you get married, a fruit called Ranka grows on a tree, and out of it pops your baby. What makes it far weirder is that sometimes the Ranka fruit gets blown across the sea and implanted in a Japanese woman - this is how the central character of the anime, Youko Nakajima, would have born, though she thought she was a normal Japanese girl until she was taken by force from her high school. In addition, royalty and other immortals can't marry - and since Nakajima becomes a queen, that includes her - and so they can't have children unless they were married before they become immortal.

Comic Books

 * The X-Men have fought The Brood, a race of intelligent Captain Ersatzes of the creature from Alien. A human implanted with a Brood egg will eventually be physically and mentally transformed into a Brood, which will have any genetic-based abilities the victim had.

Film

 * Alien (see the page picture). Here's a basic description of the Xenomorph lifecycle:
 * Queen lays eggs
 * Egg waits for host (Human, Predator, Dog Etc) to come by
 * Egg opens, facehugger crawls out, jumps on host's face.
 * Facehugger hangs on to host's face for day or two, host unconscious, facehugger keeps Host alive but tightens tail around neck if attempt to remove facehugger is made.
 * Facehugger lets go and promptly dies.
 * Host acts normal for another day or two (may/may not be aware of pregnancy).
 * Chest Burster bursts out of chest, with some of host's DNA (eg; Chestburster from dog becomes Quadropedal drone).
 * Chestburster quickly grows up into either Drone or Queen.
 * If Queen, cycle starts again.
 * Although not actually alien, the creatures from the Tremors series have a bizarre life cycle that qualifies for this trope. Eggs hatch into dog-sized "dirt dragons", which transform into bus-sized Graboids; multiple bear-sized shriekers, each capable of rapid parthenogenesis, burst from the mature Graboid; mature shriekers pupate, then emerge as ass-blasters, which lay eggs. It's unclear whether sex is involved at any stage of the life cycle.
 * In K-PAX, K-Paxians are known to have a very painful mating experience

Literature

 * Aliens from Isaac Asimov's novel The Gods Themselves are from a universe with different laws of physics. They have soft bodies of three genders (rationals, emotionals and parentals) which reproduce by fusing at the intermolecular level. This creates a mature solid form with the fused mind of the three soft ones, which forget this little fact after the act.
 * Just to clarify this a bit, when a triad of Soft Ones "melt" (that is, mate), they temporarily form a Hard One, but don't remember that after they separate (the Hard One does, however, remember its previous periods of consciousness when it is formed again). Nonetheless, this fusion is related to reproduction, being the means by which new Soft Ones are conceived (one at a time) to grow to term inside the Parental of the triad. It's not said outright, but there is the implication that there is an order to the pregnancies so that each triad will produce at least one full triad of offspring before they grow out of the breeding stage and finally merge permanently as a Hard One. The Hard Ones are genderless and act in a parental/mentor advisory role to the Soft Ones (though the Parental Soft Ones act as parents to the babies when the latter are very young).
 * The Khommites from the Star Wars Expanded Universe can only reproduce by cloning. They also only eat dietary supplements.
 * And Selonians have one fertile female and a handful of males per 1,000 births. They're subterranean mammals; the queen and the males - presumably not from the same colony - basically do little but breed while the rest of the colony runs civilization. A little like naked mole rats.
 * Humans and Selonians can apparently be allergic to each other. Or at least Corran and that one Selonian were.
 * Falleen pheromone work on anything in the galaxy.
 * And Dathomiri women can use the Force to arouse men and then you know the rest. Teneniel does this to Luke. While he doesn't like it, he still talks to her afterward.
 * Zeltrons, Green Pink Skinned Space Babes that they are, have a sexual attraction to Force-sensitives. If there's one thing the Expanded Universe has driven home, it's that Luke got around a lot before marrying Mara.
 * Animorphs: We don't learn much about the actual workings of it, but Yeerks require three individuals to reproduce, and none of them will survive.
 * The Skrit Na are even stranger. The "Skrit" look sort of like giant roaches and are fairly stupid. At some point during their lives they spin a cocoon, die, but then out of their dead body a Na (basically a Grey) pops out. It's never explained where new Skrit come from, but the Na certainly have a weird way of coming into this (or some other) world.
 * From Everworld: male Hetwan, though usually little more than perfectly obedient drones for their deity Ka Anor, will immediately go nuts and mate with any female they see, which looks like a living collection of guts. A collection of eight to ten offspring are born immediately---which is good, because the males rip the females to pieces while having sex.
 * Bruce Coville's stories often mention aliens having as many as eight genders, though, since he writes kids' books, the exact mechanics of this are never explained.
 * Though they can breed perfectly fine with humans, Martians in the Barsoom series lay eggs for some inexplicable reason. Yes, even the Half Human Hybrids.
 * When asked, the Puppeteers of Known Space say they have three genders, but its not quiet accurate. What they have is a "sperm depositor" male, an "egg depositor" male, and a nonsentient female belonging to a related species (in the same way humans are related to monkeys). The Puppeteer ova is deposited in the flesh of the third species, the egg is then fertilized, and when the egg hatches, the infant puppeteer eats its way out of the body of the "female", like a digger wasp.
 * The Doctor Who New Adventures novels published by Virgin suggest that Time Lords are all sterile and are "born" from a "Loom", a machine in their giant sentient semi-organic family Houses. Each Loom weaves Family members according to a common template, ensuring that they're related; every Family member is a genetically a cousin to each other. This is ignored, if not outright contradicted by the TV series when it resumed airing.
 * In Iain Banks' The Culture the Azadians have three sexes: Males with testes and penis, an intermediate ("Apex") sex with a reversible vagina and ovum, and a female sex with uterus and a retrovirus that slightly modifies the implanted egg.
 * Ender's Game: Pequeninos. To reproduce, the male has to turn into a tree. Infant females are brought to the Fathertree and crawl around on its bark, absorbing sperm through its dust. Also: any female that survives to adulthood is completely sterile; the young eat their way out of the infant mother's body. Both male and female young are nursed in the Mothertree, which is what happens when a sterile adult female turns into a tree, which exudes a highly nutritious sap the young feed on until they're large enough to walk around on the ground.
 * All native life on the planet is like this (for example, there are no male herd animals--the grass they graze on fertilizes the females). They were changed by a virus, brought to their planet by other alien species. All species who didn't develop bizarre reproductive cycles died.
 * Vonda N. McIntyre's Starfarer series has the squidmoths, who are born male. The males exchange sperm packets with each other and keep the packets they receive (the packets can stay fresh for a long time). At some point the male consciously chooses to undergo a metamorphosis which turns him female, consumes the collected sperm packets, lays eggs, and dies.
 * The alien city dwellers from Blind Lake have two stages in life. The sentient adult form is neuter and has a special feeding apparatus which the parasitic larval form require in order to survive. It's the larvae that actually do the breeding. On occasion, a larva is infected by the virus present in the adults and will transform into an adult itself.
 * The mantis-like Ki! from Chess With A Dragon are hermaphroditic parasitoids, who implant eggs in "host-grubs" of various non-sentient species.
 * One of the Star Trek: The Captain's Table books presented the Anjiri and the Nykkus,  two species of Reptilians whose gender (female, male, neuter) was determined by the temperature at which their eggs were incubated. Originally, they were presented in a fairly straightforward Planet of Hats way- the Anjiri were matriarchal, with the females running the planet and the males being basically incompetent Space Pirates; the Nykkus were initially presented as a sort of Henchmen Race to the Anjiri. It later turned out that   Oh, and incubation temperature also determines, or at least strongly influences, both intelligence and physical strength (with females being the strongest/smartest for each race).
 * The Phagors from the Helliconia trilogy have a cyclical libido, such that males are compelled to mate once every few days. They barely ever think about sex otherwise, yet the fact that such matings are conducted without any pretense of privacy, just as a human might sneeze in public, leads most humans to consider them lustful perverts.
 * The life cycle of the Tyr in The Madness Season proves important to the plot of the book.
 * There is a lot of this is Piers Anthony's Cluster series; every species has a different, exotic way of breeding, and of course the hero, as he Body Surfs between the species, experiences them all. Perhaps the best example not covered by another trope is the Spicans: they have three sexes, and whenever all three are present in the same area, mating will occur- not might, will. There are three roles that can each be assumed by any of the three sexes, and the gender of the offspring is determined by which sex takes which role.
 * The Rozes, troll/giant hybrids from the Garrett P.I. series, claim to be "triplets with different mothers". Garrett has never been inclined to ask for details, so we don't know if it's this trope or a cultural thing.
 * The stsho from the Chanur Saga have three different sexes and form mating trios instead of mating pairs. None of the sexes can exactly be called male or female, since a stsho which fills the young-bearing role in one trio can simultaneously fill a non-young-bearing role in a different trio. Nothing beyond that is known, since the stsho are an extremely private and xenophobic race which refuses to share details of their biology with any other species. For further strangeness, sufficient psychological stress can cause a stsho to spontaneously change sex.

Live-Action TV

 * Star Trek has plenty of examples, having been on TV for so long:
 * The Vulcans have "Pon farr", a mating season every seven years, where the male must mate or he'll die. Alternatively he can beat another male to death, which is just plain weird.
 * Xyrillian females can impregnate human males without the human noticing.
 * The Q can chose to have sex by touching fingertips, but being nigh-omnipotent that's not saying a whole lot we don't already know from the "omnipotent" label.
 * The Varro mate for life, and to ensure this they intermix their body chemistry, causing symptoms of physical withdrawal if a mate leaves.
 * All we know about Klingon sex is that it's not uncommon for both partners to break bones. Ow. A broken collarbone on the wedding night is a sign of good luck. Of course, given how Klingons tend to act, that might simply be a cultural tendency towards very rough sex.
 * The Taresians are born 90% female and claim to reproduce by implanting embryos in the wombs of females of other species, but the child will be fully Tersian. The truth is even weirder: They spread a retrovirus that turns males of other species into pseudo-Teresians, and then he's driven to return to the planet where they'll extract his DNA, fatally.
 * The Vissians have three genders, the third of which is a "Cogenitor" which contributes no genetic material to the child, but provides an enzyme which is required for conception.
 * Female Ocampa go through "Elogium", a puberty-like stage where they can successfully conceive a child (in a growth on their back), but it only happens once. Also leads to a very large bit of Fridge Logic, every Ocampa female can only conceive once, and multiples births seem to be rare to non-existent....so if every female Ocampa can only produce one child in their entire life.....how is the species not extinct already? The Fridge Logic factor of Ocampan reproduction goes far further than that: Despite only being able to reproduce once and only living for nine years, the females have constantly engorged breasts. The reason why humans have breasts and dogs don't is because we can reproduce whenever we feel like it - there is no biological reason why they should grow breasts a good four years before they can conceive. Secondly, they reproduce through a bizarre system of massaging feet and gluing their hands together for an entire week using a thick, sticky mucus - in the wild no creature could do this without being eaten by predators. This would logically mean both the males and females have nothing between their legs and are around about the same size - if this was real life and not being played by human actors and actresses the only way to determine a male from a female would be those anomalous breasts.
 * Denobulans have a mating season, and their breeding drive is regulated by powerful pheromones generated by their females. Males can become violent under these pheromones' influences. Culturally, they practice group marriage, and also remain promiscuous outside such formal relationships.
 * The Kobali resurrect, and genetically alter, the corpses of other species.
 * Andorians have four genders and need to form a telepathically bound quartet comprised of one of each gender before they can hope to conceive.
 * Babylon 5's Centauri have six prehensile tentacles for sexual organs, which are flexible enough to snake under a poker table and pick up a card on the other side of the table. There's also the Pak'ma'ra, who (according to Usenet postings by the creator) have tiny non-sentient females who live in a hump on the back of males. Finally, Ivanova tricked one alien into believing that a strange dance and a nonsensical chant was Bizarre Human Reproduction.
 * In Alien Nation, three Newcomers are required to make a baby: a male, a female, and a binnaum who catalyzes the impregnated female. Part way through the pregnancy, the female transfers the fetus to the male, where it slips inside his belly somehow and attaches an umbilicus to one of the male's nipples. It is the pregnant male who gets to have the wacky Born in An Elevator scene at the end.
 * In the original V miniseries, Willie recognizes Robin is pregnant because she's developing a ring of discoloration around her neck, which suggests that such rings are normal for Visitor mothers-to-be. His comments imply the ring becomes more complete as the pregnancy progresses.

Oral Tradition

 * The Greys are apparently extremely interested in human sexuality for some reason, so we are ourselves a case of Bizarre Alien Reproduction, inverting this trope among UFO nuts.

Radio

 * We're never told the details, but the Betelgeusians Ford Prefect and Zaphod Beeblebrox in The Hitchhiker's Guide to the Galaxy share three mothers (with the implication that Zaphod at least has more mothers who they don't share), which makes them "semi-cousins".

Tabletop Games

 * Dungeons and Dragons includes multiple examples, mostly among the Aberration creature type.
 * Illithid Elder Brains (composed of the disembodied brains of dead illithids) asexually produce eggs in pools of water. The eggs hatch into tadpoles that cannibalize each other until the survivors reach maturity. Mature tadpoles are inserted into living adult humanoids to devour and replace the nervous system. This results in an adult illithid.
 * Beholders also asexually reproduce. After becoming pregnant, they gorge themselves until the fetuses become too large and pinch the esophagus shut. When the children come to term, the parent vomits up its entire uterus (which does not regenerate).

Video Games

 * The Real Time Strategy Achron has the Grekim, a race of Time Travelling alien cyborg squid with three genders (octo, pharo, and sepi). Any two members of different genders may 'progenerate' a member of the third gender. The exact details of this process are unclear, but it does not seem to require direct physical contact, although a certain amount of proximity is still needed.
 * The Galka in Final Fantasy XI are an all-male race. They reproduce by "reincarnation", whatever that means.
 * In Mass Effect, Asari reproduction is based on 'melding' - during said process, the asari scrambles and changes up a DNA sample of her own, using the DNA of her partner, whatever sex and (sentient) species it may be, as a map/inspiration. The randomized version of the asari's genes is then combined with an unchanged sample of them for purposes of producing offspring. Physical contact is not required, but not uncommon. Even more weirdly, mating within their own species is discouraged in order to avoid certain extremely nasty genetic defects that can occur from such a union.
 * Much more disturbing with
 * You create new individuals in Patapon by burying certain materials under a special tree.
 * In an old Maxis game, Unnatural Selection, genetically engineered creatures reproduce via "melting into a skin colored blob, combinating and laying a baby version of themselves" you can watch this here.
 * The tiny Pikmin apparently reproduce by bringing plant matter and insect corpses back to their hives/'onions', which spits out seeds that first plant themselves into the ground, mature for a while, and then get uprooted as new baby Pikmin.
 * While it's All in The Manual, Gears apparently lay eggs or the children come out in a protective cocoon they later hatch out of.

Web Comics

 * In Homestuck, the Trolls reproduce by "mixing genetic material" with their lover and their archenemy in separate buckets pails, and then giving the material to a drone. Gender is irrelevant to reproduction. All of the combined material is then basically mixed together, and a mother grub takes the best material and lays eggs for the whole species. As said in comic, Trolls sure are weird!
 * This has the side-effect of making pails (and pictures thereof) Not Safe for Work among trolls.
 * And also making this video completely hilarious.
 * Sam Starfall from the comic Freefall is a Sqid. Only a small number of Sqid are fertile, and those breed early. Upon breeding, both the male and female die. A litter of young is born and, Sqids being scavengers, the Sqidlings have a ready-made food source. Other adults come along and pick Sqidlings to raise (a process described as being like picking a puppy). These "Mentors" raise the young Sqid in their race's ideals of chicanery and stealing everything not nailed down or on fire.
 * The title character of Schlock Mercenary is a carbosilicate amorph, essentially a race of organic data-storage systems turned sentient. They typically reproduce by splitting off a part of themselves that contains their personality, and merging it with that of another. On top of that, due to the "sentient data-storage" bit, it's also possible to reproduce with non-amorphs through a period of observation - a process Commander Kevyn compared to marriage. On top of that, two amorphs battling it out usually results in, rather than one or both parties dying, a single amorph with merged personality traits of both combatants.
 * Also in this 'verse are the Qlavo, who conceive normally with males and females, but hand off responsibilities of development to a third gender, muftales.
 * El Goonish Shive has Uryuoms, whose natural way of reproduction allows an arbitrary amount of genetic parents to a single child, that doesn't even need to actually include Uryuoms themselves - in addition to other biological weirdness.

Western Animation

 * Kiff from Futurama gets pregnant by touching someone.
 * Kif's species (Amphibiosans) become receptive to DNA transfer (impregnation) when they develop a strong emotional bond with someone, their smizmar. DNA is transferred through touch, and presumably any species' DNA is compatible. While in the episode in question the biological parentage gets mixed up, the smizmar is the "true" parent.
 * Dr. Zoidberg's species lay eggs into the ocean and then die off en masse. He's only lived so long because no female seeking a mate will even look at him. This doesn't prevent Zoidberg having a Jewish Mother-equivalent relative, so presumably some Decapodians avoid mating to raise the kids.
 * There was an episode of the 90s X-Men cartoon where Rogue was almost turned into a Queen for the Brood, an alien race which breed by basically infecting other species and turning them into one of themselves. However, Rogue touched Wolverine, borrowing his Healing Factor and returned to normal.
 * The French/Chzech cartoon Fantastic Planet features the Draags. When the Draags wish to reproduce, they go into a meditative trance, which causes a spherical forcefield bubble to form around them as they float up into the sky toward their planet's moon. Upon reaching the moon, they land on gigantic, headless Greco-Roman statues, which proceed to dance the waltz (no, really, that's all they do).
 * In all fairness, that could have just been foreplay - the Oms (humans) did sort of start destroying the statues mid-dance.

Real Life

 * Many of the above scenarios were based on the life cycles of Real Life organisms. Ichneumon wasps implant eggs in host species, eusocial insects have a reproductive caste, microorganisms physically merge when mating, plants alternate generations, and internal parasites (e.g. liver flukes) make all the above examples seem routine.