InuYasha's father and mother. The Inu no Taishou does have a human form, but his true form is the size of a mountain.
Dragon Half features, unsurprisingly, the offspring of a human and a dragon. She basically looks like an adorable teenage human girl with horns and a tail, she's super strong, and her name is Mink for some reason.
Princess Vina too. When you're tired of looking at her humany cuteness, drop a heavy weight on her and go “Aw!” over her slime-moldy cuteness.
Both of those involved shapeshifting from a non-human into a human form. Vina was born as a slimemold, she had to learn magic to change into something humanoid.
In One Piece, there are people called "Wotans", a hybrid race of Fishman and Giants. While Fishman are generally taller than humans, Giants are dozens of feet tall, which brings up a intresting question of how that works.
The Fishman Island arc has the union of the merman King Neptune and the mermaid Queen Otohime, who are roughly giant-sized and human-sized, respectively. Otohime then somehow gave birth to Princess Shirahoshi, who even as a baby looked about 10 times as big as her mother. Even if we concede that mermaids lay eggs like fish do, there's no way she could have laid something as large as Shirahoshi, not to mention that a pregnant mermaid is depicted in the background of one episode.note Unless Shirahoshi simply had a hell of a growth spurt during the months following her birth, but that's a big stretch.
Fishman and mermen in general have this trope to an extent, as they never seem to mind what species of fish they're based off of. And their genetics keep past generations in memory for much longer than humans'; a pufferfish fishman and a wolffish merman have been shown to be brothers.
In a Johnny the Homicidal Maniac sidestory comic, some really, really stupid aliens visit Earth and force a man to Mate or Die with a chicken in order to study human reproduction (they thought the chicken was a human female... Did we mention they were really stupid?). The result are freakish half-human half-chicken hybrids, with the details of their conception and gestation being blessedly skipped over by the story.
Firebreather stars the offspring of a pairing between a human woman and a giant dragon, which resulted in a scaled, orange skinned, four-fingered, but essentially human-looking offspring. She tried to explain how this happened, but we don't know because her son covered his ears. Apparently it was quite simple.
The minor Marvel character Epsilon Red is only able to survive in a vacuum. Shaky science, but fair enough so far. In a flashback (set well after he was turned from an ordinary human into a spaceman), his wife is shown to be pregnant. Think about that for a moment.
Smax from Top 10 is the child of a yeti-like ogre and the warrior-woman he captured and raped. She may have survived the pregnancy... if she didn't have twins.
Briefly mentioned in Runaways, when two characters discuss the possibility of a normal-sized woman getting impregnated by Galactus. He's not the father. Ultron is.
Les chroniques de la lune noire (blackmoon's chronicles) is a French comic with moderate international success. What interests us here is Ghorghor Bey, who is several meters tall and half-human, half-ogre. One could only wonder how his parents had sex, until Ghorghor got his own spinoff where it was revealed that his mother was raped by a young ogre during a pillage.
Late in the story, Wismerhill gifts Ghorghor a ring that allows him to shrink at will. The only point of this gift was allowing him to have normal sex.
An issue from Alan Moore's run on Swamp Thing has a humungous technoorganic Living Ship using Swampy's genetic material to create half plant/half machine hybrids.
There exists a Chronicles of Narnia fanfic in which there were many not-oblique-enough references made to Ettins (akin to extremely large orcs) who abducted humans (men, surprisingly) in order to produce magically-viable offspring, since generations of inbreeding and incest had destroyed the health of the Ettin line. The abducted humans usually didn't survive much past the experience.
Hivefled involved the Grand Highblood doing terrible things to Gamzee, and then helpfully provided a size comparison chart. Keep in mind Gamzee is tiny for even a pre-final-pupation purpleblood, but noticeably bigger than most young trolls. Ow. GH also regularly has consensual sex with Condesce, who isn't much bigger than Gamzee; at least they had thousands of years to practice.
In Pony POV Series Dark World, Rarity and Spike are an Official Couple, with Spike now being a full grown dragon and far larger than she is. Loose Canon taking place after the series is over has other characters lampshade it with some level of Squick involved. Spike implies Rarity's ascension to Alicorn status has something to do with it.
A flashback to the time when Luna became Nightmare Moon also shows a half Dragon half pony hybrid, showing the two species can actually mate and produce offspring. In the same Loose Canon as above, it's shown that Rarity actually ends up pregnant with Spike's child.
One script of Galaxy Quest has this ending for Fred and Laliari. Thankfully this was not shown. (Laliari is a Thermian, a species of Starfish Aliens who look like an octopus eating a squid. She uses a hologram to "dress up" as human, but apparently takes it off to have sex. "Ohhhh that's not right" indeed!
In the movie Splice, at the climax the human/multi-animal hybrid Dren, a teenage female in physiological age, engages in this with her father. Needless to say, a major cause of Squick.
In Meet the Feebles by Peter Jacksonnote Yes, that one, an elephant named Sid is said to have had sexual relations with a chicken. Said chicken then brings up a paternity suit against Sid, who claims the baby isn't his ("She slept with half the chorus!"). It becomes apparent, however, that the baby was, in fact, fathered by Sid, as it's seen that the baby is a cross between a chicken and an elephant.
Also the boss of the theater (a walrus) is having an affair with his secretary (a cat). On screen.
In Jackson's Dead Alive, the backstory of the zombie plague involves diseased rats raping monkeys in Sumatra, creating the undead and contagious Sumatran Rat-Monkey.
Shrek 2, at the very end, shows Dragon and Donkey's offspring. According to the action figures, they're called "Dronkeys". They're pretty strange-looking, too. Amusingly enough, the gag started life when the first movie came out, as a short comic in a Mad Magazine. The animators probably thought "Why the hell not?"
Timon: Listen to me! The problems of a couple of wacky kids like us don't amount to hill of termites in this nutty circle-of-life thing. And so I ask you: If not now, when? If not me, who? I'm lonely...
Given how real-life Hyenas work, he'd be in for a surprise...
In Ralph Bakshi's Wizards, Elinore is a human size half-human/half-fairy. Her mother was a fairy. Ouch.
In Glen Cook's Garrett, P.I. books, the main character's homeland of Karenta is full of this. Because the human empire is at war, many jobs have been filled by various creatures (trolls, dwarfs, elves, etc), all of which seem to be able to breed with each other and humans, sometimes in such variety that it's impossible to tell exactly what a creature is unless you know their great-grandparents.
In the Xanth novels, any two species of creature are capable of breeding and having viable offspring. This is due to the abundance of unmarked, naturally occurring Love Springs, which (generally) cause unsuspecting people and animals who drink the water to immediately and involuntarily mate. It also magically ensures offspring. The result is either Mix-and-Match Critters like a centaur or a werebeasts of some sort. All of the chimeric creatures in Xanth, such as mermaids, are literally the result of interspecies breeding. As this is a rather abrupt and off-putting experience, so those cross-species couples actually interested in enjoying the experience generally use 'Accommodation Spells'. Perhaps the best example of this is the case of Becka from Dastard. Her mother was a young maiden who fled into water while being pursued by a dragon. As it turns out, the water was a Love Spring and the dragon was a male... Becka is an example of the were-creature phenomenon, being able to swap between cute girl and hand-chomping dragon forms.
In Harry Potter, Hagrid's mother was a giantess (in this universe, violent, 20-foot-tall humanoids) and his father was an ordinary, if somewhat short, human wizard. In the fourth book, he asks Madame Olympe, another half-giant, which one of her parents was the giant - so apparently, some females managed. Hagrid himself also bred manticores (creatures from Persian mythology with the head of a man, the body of a lion and the tail of a scorpion) and fire-crabs (tortoises with jeweled shells that shoot fire out their rear ends) to produce blast-ended skrewts, which resemble 10-foot, headless, armored scorpions that move by jet propulsion. In this case, more than justified by A Wizard Did It (albeit a failed one).
In the Potterverse, cross-species breeding is strictly monitored by the Ministry of Magic, and experimental cross-breeding without Ministry supervision is a criminal offense.
A Song of Ice and Fire author George R.R. Martin apparently had the same mechanics-related thoughts. In the far north of Westeros, humans are occasionally abducted by giants. Abducted men have produced half-giants who have since further interbred with humans. The abducted women... don't survive.
There is a rather horrid image in Sir Thomas Malory's Le Morte Darthur about a giant who has abducted the Duchess of Brittany: he hath murdered her in forcing her, and hath slit her unto the navel.Squick!
"The Dunwich Horror" is itself a Shout-Out to Arthur Machen's The Great God Pan, where the eponymous deity impregnates a woman who was surgically modified to be able to perceive Him in all His glory, and was instantly driven insane by the experience. The child was physically more human than in Lovecraft's tale, though.
In the Discworld novels the reason for all the Mix-and-Match Critters in heraldry is because the heralds insist on drawing all the designs from life, and there's not really enough space to keep all the animals, so they get a bit... close.
Guards! Guards!! has the swamp dragon Errol and the "king". Errol can sit on a person's shoulders while she weighs several tons and was once mistaken for a castle turret. They're not properly speaking of the same species, but they are at least of related species, and some real-world species show sexual dimorphism almost this extreme.
It's mentioned in Snuff that an unnamed dwarf and troll have set up housekeeping together. Perhaps fortunately, Vimes is cut off before he can ask the inevitable question...
While actual offspring aren't mentioned, Nanny Ogg's tomcat Greebo is infamous throughout Lancre for being eager to fight and/or rape pretty much any wildlife he encounters, up to and including a she-bear which was innocently digging for roots.
The hero of Tad Williams' The War of the Flowers is shepherded through Faerie by, well, a fairy. Several times people assume they're boyfriend and girlfriend, squicking him out. He later asks how such a relationship would even be possible. The answer? "Surgery." This was a Magitek universe, so this was not a flippant answer. The surgical/sorcerous procedure which could accomplish the deed was a significant plot point. Eventually, the tiny fairy does hook up with a much larger character. They have tentative plans for him to have the compatibility surgery, since it's easier going "from large to small". The hero still had trouble processing this information.
One of the books in Mercer Mayer's Little Critter series entitled "Just a Little Different" has a character that has a turtle father and rabbit mother.
In Dr. Seuss's Horton Hatches the Egg, a half-elephant, half-bird was created by the titular elephant sitting on a bird's egg.
In one of the books in Christopher Stasheff's A Wizard in Rhyme series, the wizard encounters a Dracogriff: the offspring of a male dragon and a female griffin.
The Star Wars Expanded Universe has Sith alchemy, which explains why so many species are variants of humans (and presumably capable of playing HSOWA straight), as well as why species hold physiological elements of vastly different taxa, e.g. Mon Calamari having elements of both mollusks and arthropods. Or Falleen having elements of both reptiles and mammals. Basically the Sith were really big on HSOWA.
The half-human, half-bird Quetzals in Flora Segunda are said to be the result of human women mating with male eagles. Even in a world with magic, it's hard to figure out how that one would work.
In Mary Brown's Pigs Don't Fly (But Dragons Do) the protagonist ends up making love to a dragon, who to be fair was transformed into a human for a time, but it is later revealed that he was transforming back and forth during their time together. This results in a pair of half-dragon twins being hatched by the end of the book Draggone's Eg.
The Golden Flower Pot by E. T. A. Hoffmann is a story of a human who fell head over heels for a magical creature looking mostly like a blue eyed gold-green snake and sometimes like a human lady — a daughter of a salamander and green snake. The green snake, in turn, was a daughter of Lily and Morning-wind. The main antagonist of the book is the child of a feather from a dragon (slain by the Morning-Wind) and a sugar beet. Fairyland family trees can induce vertigo like this.
His other books had all Alchemic Elementals trying to know a human closer. And one young man manipulated into unknowingly trying to romance a clockwork automaton.
Song in the Silence by Elizabeth Kerner is about a woman who, on first meeting a house-sized dragon, discovers that she possesses the capacity for Truespeech (dragon telepathy). She and the dragon fall in love they can never consummate and wrestle with the implications of this trope until the dragon is killed and mysteriously reincarnates in humanoid form.
In Reamker (a Cambodian poem based on Ramayana), Hanuman, a vanara woos Sovanna Maccha, a mermaid. They eventually had a child who is a half-vanara half-mermaid.
In the Merry Gentry series by Laurell K Hamilton, one of Merry's partners is the son of a female (human-sized) sidhe and a male (doll-sized) pixie. Merry herself also participates in non-reproductive sexual acts with several (doll-sized) demifae.
Averted in Animorphs, due to the morphing technology that allowed Elfangor to take human form when he conceived Tobias with Loren.
Varley's Titan series features Titanides, creatures biologically engineered by a gigantic half (or more) mad alien, specifically based on human mythology. She gives them three sets of genitalia: a horse-sized male and female set on the horse half, and a human-sized male or female set "in front". They are cross-fertile with humans, at least with the front set: Gaea (the alien) is exceptionally good at biological engineering. The cross-breeds are ... peculiar, having the basic centaur body but with human feet instead of hooves, or even stranger combinations.
In Dean Koontz' urban fantasy mystery The Haunted Earth the plot is driven by the offspring of a terrestrial god and an alien god, one of whom manifests as a storm.
In a nod the "The Shadow over Innsmouth", Jennifer Morgue brings us human/Deep One hybrids. The deep ones themselves are alien fishmen, but some of the human hybrids can be startling attractive (which helps when breeding with humans, of course), and the protagonist muses that he now understands why some people take to solo nude snorkelling off secluded beaches...
Reference is made to the rather fishy-looking and ugly residents of Innsmouth from the original story, and they are implied to be a particularly in-bred group, and would look pretty peculiar even in the absense of Deep One genes.
Similarly, in Xena: Warrior Princess, human female Ephiny marries and has a child with Phantes, a centaur male. The child is named Xenan and grows up to be an ally of Xena's.
In the final episode of Lexx, the titular Living Ship, dies of old age, but not before giving birth to a smaller newborn ship. The other parent that helped produce the offspring was a dragonfly. A normal dragonfly from Earth. Forget Skitty and Wailord, inches long insect and Manhattan sized insectoid spaceship is way more bizarre. It helps that the ship is the woman in this situation.
An episode of The Golden Girls featured the character Rose dreaming of a peaceful, Utopian future, one where bears would live in harmony with field mice, "But they wouldn't be able to mate or else the field mice would explode."
In Eureka, Deputy Andy, an android, has sex with SARAH, the AI of Carter's house. While they could have averted this by just using the finger uplink gag they used in the beginning of the episode ("wrong port"), Andy instead comes walking out of a random door as he zips up his pants. Carter and Jo can only stare in confusion.
In Buffy the Vampire Slayer all but the True demons are apparently partially mortal, and many have inferred this means that there was actual breeding going on between them. This seems physically problematic. Two True demons have been seen - Olivikan, an enormous armored insectoid snake creature, and Illyria, a massive, taloned, armored creature with, admittedly, tentacles. Nevertheless, how exactly either of them would go about breeding with a human raises a few questions.
Not necessarily - vampires for instance were specifically said to be half-human hybrids because the last demon to leave Earth infected a human with its DNA, thus creating the first vampire (probably a Turok-Han). Other humanoid-ish demons might similarly be the results of viral-infection type "breeding" between true demons and early humans.
Whistler, who was introduced in season 2 as a half-demon hybrid, reveals in the season 9 comics that his parents were a pure demon and one of the powers that be.
Averted on Roswell, where a certain type of organism was used to manipulate the human and alien DNA and allow the creation of the human-Antarian hybrid children.
Implied in Tracker, given that Mel is revealed to have Cirronian ancestry.
In The Goodies Graeme crossbreeds dogs with other animals and then somehow dogs with household furniture in the episode Frankenfido.
Dr. House asked this question flat-out of a patient who was a midget married to a normal-sized man. "He put me on top of him and spun me like a top," was her reply. Her daughter was in the room at the time, and a markedly revulsed look crossed her face.
How true this was is up in question, as at the time, said midget was deeply entrenched in the Snark-to-Snark Combat with the good doctor.
One episode of Tales from the Crypt revealed that the Cryptkeeper's parents were a deformed human male and a female mummy, who encountered one another in a sideshow.
The novelty song Buntz! tells of a highly acrobatic tryst between a British ship's-mascot dachshund and a classy female Afghan.
"But now throughout France a new dog breed abounds:"
"The famous Marseille Afghan short-legged hound!"
Fatally averted in Little Gomez, in which the randy chihuahua's St. Bernard paramour got bored (and sat down) just a bit too soon.
The song The Dragon's Lamentable Love, about a woman and a male dragon.
"True love died 'cause nothing fit. That's the long and short of it."
The Minotaur was born of this sort of a union. King Minos angered the sea god Poseidon by refusing to sacrifice a bull (given to him by Poseidon for that very purpose), so Poseidon cursed his wife Queen Pasiphae to fall in love with that same bull. Don't think too hard about the mechanics of this.
Not being human probably helped, Pasiphaë was the daughter of Helios and an ocean nymph
Zeus, that philanderer of mythological proportions (pun very much intended) often seduced human women in the guise of animals, such as a bull or a swan. Or a shower of gold.
Aphrodite who was born out of foam on the waves when Cronos — Zeus' Father — threw Ouranous's, HIS father's, penis and testicles into the sea. So Aphrodite's birth is not only mind-boggling, it also shows her to be a generation older than Zeus and his siblings. Presumably her mother is Thalassa, an obscure female personification/goddess of the sea.
The origin of the centaurs takes the cake: Ixion was invited to Olympus by Zeus. Zeus created a cloud-woman named Nephele that looked like Hera to trick Ixion. Ixion had sex with Nephele, who gave birth to Centaurus. Centaurus, deformed and outcast, lived alone on Mount Pelion and had mated with the mares that lived there, producing centaurs. And now you know!
The original Antlion was the child of a male lion and a female ant.
The Bible may or may not features this (depending on your interpretation) in the form of the Nephilim. Angelic fathers, human mothers.
In Egyptian Mythology, there was a minor fertility goddess named Tawaret, who herself was a mix-and-match-critter (she was part lioness and part hippo, with some attributes of a human female). And she, being a fertility goddess, was nearly always pregnant...and her consort was Sebek, who took the form of a crocodile. (Who was depicted variously as traveling on her back...or even literally a part of her.) Her Darker and Edgierinverse was the demoness Ammit, who devoured souls deemed "unworthy" when measured against the Feather of Ma'at.
Genbu, the Guardian of the North, winter, water, and a minor association with fertility...consists of a giant tortoise having sex with a giant snake. (May or may not be consensual sex, depending on whom you ask.)
In the mythologies of several ancient European civilizations, though it's often attributed to Greek, you have the basilisk. It is hatched by a rooster from the egg of a serpent or toad. Depictions range from giant snake (it is the King of Serpents, after all) to various snake/rooster combinations.
On the flip-side, you have the cockatrice, which is created when a toad incubates the "egg" of a rooster. Depictions are similar to those of the basilisk, though they tend more towards either direct fusion (first half and legs are rooster, back half is serpent) or winged dinosaur-like forms.
In one Bloom County arc, Hodge Podge and Rosebud, respectively a jackrabbit and "basselope" (basset hound/antelope) had jackabasselope children.
The Iron Sheik, gentleman that he is, once related in an interview about how he walked in on Andre the Giant having sex with an normal sized woman. He likened it to a "bear fucking a rabbit, if the rabbit could get on top."
The dragons of Dungeons & Dragons can change shape into nearly any living creature, and can mate with anything into which they change shape to produce viable half-dragon offspring.
Some dragons can change shape like that. Others... well, sometimes A Wizard Did It (merging traits from two species doesn't always mean there was any mating involved. Just look at most of the origin stories for the owlbears), sometimes the dragon could have changed shape by learning spells that allows changing shape, and sometimes no explanation is provided.
The increased amounts of splat books have brought increasingly outlandish (and Squicky) variants of the above half-dragon, such as the half-infernal and half-celestial, the half-troll, the half-illithid, and even the half-golem (though the lattertwo have nothing to do with parentage). Most of these, being templates that are applied to other creatures, have far too few limits on what they can be placed on.
Several editions of the game have talked about the fecundity of goblinoid races, which include goblins, hobgoblins, ogres, and orcs. They could easily interbreed with each other, with humanity, and with several other species. It seems that developing new monsters for the game mostly consists of finding two creatures already in the game and figuring out what happens when they have sex.
See also the Book of Erotic Fantasy. Yes, it's a real book. (though unofficial) Or "The Complete Guide to Unlawful Carnal knowledge" (includes rules for hybrid children, critical hit rules for Groin Attack and "Porno periodical for humanoids" treasure tables). Or "Nymphology. Blue Magic." (Mongoose Publishing, Encyclopaedia Arcane series). Invariably contains mix of Fetish supplements, Mix-and-Match Critters close-up supplements, things You Do NOT Want To Know (whoever you are) and lots of jokes.
The Book of Erotic Fantasy actually has a friggin' TABLE for this kind of thing. Complete with cloud giants and 1" tall sprites interbreeding. Brain Bleach now, please?
But the real kick is that you can have a half-dragon dragon. Pink dragons (half-white reds or half-red whites) are especially powerful, as the template changes natural cold/fire vulnerability into immunity.
An electrum dragon (half-gold, half-silver) would do the same deal... Except not be evil. And pink.
Back in the 1st Edition era, a Dragon article inspired by artists' color wheels proposed that the standard-issue green dragon already is a product of this trope, having arisen when blue dragons mated with yellow ones. Statistics for yellow, orange, and purple versions of chromatic dragons were included.
Humans also seem to be able to breed with many things as well. When a Half-X is a race and not a template, the "Half" is assumed to be human.
Green Ronin sourcebook "Bastards and Bloodlines" contains guidelines for turning anything into a half-template. Yes,anything. The cover of this book features a half-illithid drow (with both exposed cleavage and a bare midriff). It includes the half-beholder template. The first three creatures in the book are the Alicorn (Elf/Unicorn), the Aellar (Elf/GIANT EAGLE) and the Blinkling (Halfling/BLINK DOG). It is a very strange book.
Speaking of dwarfs and elves, Myth Drannor was named so "In deference to a visionary elf of old who found the love in him to marry a dwarf". And yes, in Forgotten Realms dwarfs of both sexes have beards, elves of both sexes don't. This one isn't too hard to imagine; unimagining it is another question. Elaine Cunningham's take on this particular combination you may see here.
Of course, the experimentation justification can't be used for the Draegloth, a product of hot Drow priestess on Glabrezu action. What makes this one especially squicky is that Glabrezu are incapable of altering their appearance, meaning that someone had consensual sex with a hideous, giant, four-armed, pincered, dog-faced, unholy abomination of the universe. One of the Drizzt Do'Urden novels actually not-quite-shows this happening. In Menzoberranzan (at least) the 'valedictorian' of each class of priestesses is accorded this 'honour' as part of the graduation festivities; indeed, Drizzt's sister partook of this herself when she graduated (though thankfully without 'offspring'), and considers "It brought me power" to be justification enough - before, during, and after. Thoroughly Squicky, even though the 'action' takes place off-screen.
They're drow, the only people who find "more power" to be a more thorough justification than Tim Taylor.
And the War of the Spider Queen series finally proved that the presence of one Draegloth is all that needed to not only turn a bunch of bickering, scheming, backstabbing drow on a mission for the sake of Religion of Evil into a party of rather likeable characters, but also do the same for another half-demon and half-shadow dragon half-drow. There are bastards, and there are... bastards.
There's an entire House of Gold Elves who not merely played with this, but had crossbreeding program, so now it consists of Daemonfey (half-fiends) and Fey-ri (tieflings). Apparently, old elven villains could be "outbastarded" only in a literal sense... The survivors of House Dlardrageth are balor's daughter Sarya, her son from a vrock Ryvvik, and son of her brother and a marilith Xhalh. Three clans of Silver Elf fey-ri joined them, though these supposedly got more of succubus or incubus blood.
"The Singing Sprite" inn (Secomber) is named after its founder's wife. Because she was a sprite (as in, 2' tall winged fairy) and habitually sang atop the tables. Granted, that guy, while human, wasa wizard...
Traditionally (i.e., before 3rd Edition), humans, orcs, and ogres were all interfertile. Humans mating with either always produced half-orcs or half-ogres (who were themselves fertile with each other and all three species), but orc/ogre pairings had it differently: A female orc mating with a male ogre would produce an "orog", basically a large orc that's smarter than either of its parents, while a female ogre mating with a male orc would produce an "ogrillon", a small ogre that's less intelligent than both parents and is inexplicably covered in bony nodules that give it an armor bonus; orogs are fertile but ogrillons are not. They dropped these complicated ideas in 3E and made no mention at all of orc/ogre hybrids, but orogs did return in Forgotten Realms as simply a large subspecies of the main orc race.
All that was probably the reason for doing away with half-breed templates in 4e. Wizards of the Coast parodied the template system with a fake leaked 4e Character Sheet on April 1st in 2008 with the race entry containing "Half-.../Half-.../Half-...".
Third Edition also had "Mongrelmen", a race of we're-not-quite-sure-whats that presumably arose through interbreeding of various humanoids. A dwarf meeting a mongrelman would think he was a short elf; an elf meeting one might believe him to be a tall dwarf ... the basic rule was "a mongrelman can pass for any humanoid race except the one of the person he's talking to." A very few mongrelmen actually were hideously deformed; these were held up as examples of mongrelmen so the other humanoids wouldn't twig that that oddly-tall halfling on the edge of town was also a mongrelman.
The epic module Return to the Temple of Elemental Evil introduces half-elementals as some of the major villains, which should be impossible, because elementals are not anatomically compatible with most mortal beings. (The template says that the base creature can be "any corporeal creature with an Intelligence Score of 4 or more. This can even include some undead creatures, which normally can't sire or bear children via regular means. The module does say that magic and/or divine power is often involved in their birth as a way of explaining this complication.
Averted in the Old World of Darkness game lines, which actually had rather extensive FAQs in some of the supplementary books about what happened if various supernatural monsters got it on. Their solution? While most everything was human enough to mate, the powers you got were a spiritual rather than genetic thing, and the rules of spiritual inheritance were such that you could not have a "mixed soul". The result tended to be that the offspring would be one kind of monster without any real benefits from the other parent. (The writers of those books really hated mummified Vampire/Werewolves with Changeling powers and Mage spells, and went out of their way to keep them out of the game), although such "crossbreeding power" was hinted at in earlier editions.
The New World of Darkness has a hard-and-fast rule that no character may ever have more than one supernatural template, with various minor plot justifications to avoid questions being raised. (For example, werewolves cannot be possessed by spirits because of their own innate spiritual nature; in rules terms, they're immune because spirit possession is a different template.) There are "lesser templates" (psychic, thaumaturge, ghoul) a person can adopt while still being technically considered "mortal," but if they ever make the full upgrade to a supernatural, said template vanishes.
The Munchkin card game gives us the Half-Breed card, for Half Anything Hybrids. Elf/dwarf? Fine. Elf/gnome? Fine. Orc/dwarf? Fine. This moves into the seriously disturbing when the Dungeon of Ridiculous Races (letting you have as many races as you can find) kicks in; how does being half-elf, half-orc, half-gnome, half-dwarf, and half-halfling (quarterling?) sound? Arguably even worse are the 1/3-Breed and Chimera cards in the seventh expansion; 1/3-Breed lets you have three races, while Chimera means two or more races at all times, with the card being lost if you go below this. Whimper.
In Shadowrun, the standard fantasy races (elf, dwarf, orc (spelled ork), and troll) are explicitly said to be human subspecies. Interbreeding is possible in any combination, but children always match one of their parents (or sometimes revert to human); there are no mixtures. There is flavor text to the effect that a dwarf carrying a troll fetus would probably need major medical assistance to complete the pregnancy.
The prequel game Earthdawn added several decidedly non-human playable species, with interbreeding specifically labeled impossible (short of A Wizard Did It).
Given that (barring certain Charms) the only way for Lunar Exalted to produce beastmen is to either have sex with a human while in animal form or sex with an animal in human form, this has probably come up at least once.
There are implications that Luna and Gaia may involve this. Between the fact that Luna can shapeshift into all manner of forms (some of them truly colossal) and the suggestion that Luna only really gets fulfillment out of their relationship when Gaia's main bodies (some of which can be the size of planets) are around...
And then of course there is the Scarlet Empress and the Ebon Dragon.
The mutable nature of reality in general in the Wyld facilitates all manner of this. For instance, the most common ancestry of stone lions is the encounter between a lion and a rock.
In Into the Woods, it's heavily implied that Jack gets it on in some manner with the Giantess at the top of the beanstalk (the line is "And she gave me food and she gave me rest, and she drew me close to her giant breast"). It's also pretty clear that the Big Bad Wolf intends to rape Little Red Riding Hood. And her Granny.
It provides an extreme example with the Trope Namer: Skitty is a two-foot tall housecat-like Mon, and Wailord is a forty-seven-foot long whale. Yet because the game places both of them in compatible breeding groups, a player can pair them up and produce viable offspring of either gender. (Bulbapedia, the largest Pokémon wiki, describes the term's etymology in further depth for those interested.)
Now Wailord can breed with Dedenne, a Pokémon that stands at a measly 8 inches tall. Made all the worse by Wailord's 48 foot length...
The 718 Pocket Monsters are divided into 15 "egg groups" based loosely on biological niches, such as "Bug," "Mineral," or "Fairy." Almost all Pokémon belong to at least one grouping; male and female monsters that share a group can breed, regardless of relative size or form, and the only Pokémon not in an egg group are "baby" Pokémon, most Legendary Pokémon, and three others, two of which (Nidorina and Nidoqueen) seem to be only due to a bug that was maintained for the sake of continuity, with the last being Unown. The resulting baby will normally be of the mother's species, but may inherit moves from the father. The shapeshifting Pokémon Ditto is a special case, as it has no gender but it can breed with anyone to produce a new baby of the other Pokémon, allowing you to (for instance) get eggs from non-gendered or male-only Pokémon.
Especially odd are the kind of pairings one needs for some of the more complicated breeding chains. One chain for Ursaring (a bear) includes Heracross (a giant bug), Paras (an insect with a mushroom on its back), Chikorita (a stubby little green sauropod with a leaf growing out of its head), and Rhyhorn (a rhinoceros with rock armor plates). And, of course, you can have as the final pairing Teddiursa (which, as the name suggests, is a cute little teddy bear) and Rhydon (a huge bipedal rhino).
Gardevoir's family appears human-like but can breed with the "Amorphous" egg group. This means a human-like Pokemon can breed with a Muk (made out of pure poison and pollution), Ghost Pokemon (who are already DEAD), Slugma (which are made out of BOILING LAVA), and Rotom (which are ghosts made out of electricity). A Gardevoir breeding with any of these Pokemon without almost dying or suffering 3rd degree burns SHOULD be physically impossible. (The anime played with this a little, where Jesse's Wobbuffet - who's also in that egg group, despite the fact that it looks like a blue punching bag with stubby legs - fell head over heals in love with a wild Kirlia, the pre-evolved version of Gardevoir so much that it disobeyed Jesse to protect her. (It wasn't clear just what the Kirlia thought about this.)
A Let's Play of Mystery Dungeon also lampshaded cross-chain breeding explained above. After Jake and Sheldon rescue a Plusle and Minun pair (the latter named Hankosha) and rescuing a Magikarp (who is also named Hankosha), the Magikarp explained the Minun is his great grandson. The author then added:
Oh, and to those wondering: Hankosha + Feebas female (both Dragon egg group) = Feebas male + Marill female (both Water 1 egg group) = Marill male + Minun female (both Fairy egg group) = Hankosha. You're welcome.
The early Dragon Quest Monsters games are the lords of this trope. While monsters are grouped into families based on type, any matchup will succeed as long as the prospective parents are of opposite genders. Dragons and birds, undead and plants, slimes and animated objects, and the offspring will nearly always be something other than either of its parents. On top of that, the child will have the potential to learn all powers of its species, all powers of both parents' species, and any powers either parent knew at the time of conception, allowing for some truly evil twinking.
Dragon Quest Monsters: Joker, seems to solve the problem. Instead of each monster being male or female, they can be Positive, Negative, or Neutral, and the process is known as Synthesis. Synthesis requires a positive and negative monster, with a neutral monster substitutable for both (However, you CANNOT synthesize two neutral monsters.) Imagine the two monsters you pick being pureed in a blender, then having the concoction froze into a new monster. This could explain why you lose your monsters after synthesis.
There are multiple sub-breeds of the cat-like Khajiit, with the phases of the moons determining which one they will become. At birth they're almost indistinguishable from plain old regular kittens but what they will become as adults becomes obvious fairly quickly. They range from being house cat shaped and sized, to roughly humanoid, to tiger-likes larger than a horse. They're all still the same species, and can all breed and give birth to any of them.
In-game texts Hand Wave unions of different species, with the offspring generally being based off of the race of the mother, though traits from the father can easily be inherited. Bretons (magically-inclined humans), for example, are the result of extensive interbreeding between ancestral elves and their human concubines until the hybrid population eventually crowded the two parent races out of the region.
Oblivion even has a character who is the son of an orc and a vampire. The result is a non-vampiric, but very pale Orc.
In Morrowind there is an in-game text titled Interspecies Phylogeny which treats the subject from a scholarly standpoint.
And Ahnassi, though the relationship is only implied.
There's also an in-game text titled The Lusty Argonian Maid which treats the subject from a ... different ... standpoint. (Argonians are humanoid reptiles.)
The original The Real Barenziah in Daggerfall has a (very NSFW) scene with a Khajiit and a Dark Elf. The book appears in the later games, but said scene is unsurprisingly censored (both in-game and in-universe).
Morrowind also has an easily missable throw-away line hinting at this trope: there's a town with a strip club/brothel in it, and if you play as a male Khajiit one of the ladies working there will say something like "Not another Khajiit. I'm still smarting from the last one." If you've read the above-mentioned NSFW version of The Real Barenziah, or know much about cat anatomy, you can put two and two together.
In Skyrim, Hadvar makes a joke about this upon finding out that the Player Character is the Dragonborn (a mortal with a dragon's soul and powers).
Hadvar: "'Dragonborn', huh? Was it your ma or your pa that was the dragon?"
Acquiring colored chocobos in Final Fantasy VII requires you to breed chocobos you've captured and leveled up. Despite the squickiness, breeding their children, this a mild example and pretty much what people do in real life. VG Catsexamined this in its usual manner.
Demons in the Shin Megami Tensei games can be fused with one another, or in some games simply sacrificed, to create new demons. As demons don't gain power through play, unlike the human characters, this is the only alternative to negotiating with more powerful creatures.
In Shin Megami Tensei Imagine it's explained further, the demons lose their physical forms and their Magnetite (Energy) is fused to create a new form.
Averted two separate ways in Persona: In the first and second ones (Persona 2 is a dualogy), you simply acquire "cards" (small fragments of energy) from demons, which you then make into Personas. In Persona 3 and Persona 4, the "Personas" are just shards of your personality, not independent lifeforms.
Sonic Adventure and its sequel both include Chao gardens. Chao may be trained and any two may be crossed, with the usual Lamarckian mechanics coming into play. This doesn't affect anything outside of the garden, though.
In those versions of the Sonic storyline based on the Sonic Sat AM continuity, Sonic's girlfriend is the half-squirrel, half-chipmunk Sally Acorn. There have been a fair number of "future" scenes where the two of them are married and have kids.
The pińatas of Viva Pińata could be bred (I'm sorry, romanced) to produce offspring—this was a key point of the game. In most instances, pińatas were disinterested in those outside their own species, which avoided such Skitty and Wailord moments, but in one instance apparently-unlikely cross-species breeding could occur. The swan pińata Swanana and the pig pińata Rashberry could have hybrid offspring when certain requirements were met, producing the winged pig Pigxie. Which the parent species were apparently so ashamed of that they'd start fights with it. Even the in-game encyclopedia refers to this offspring as a horrible mistake. Unfortunately, there were only a few clues in the game as to how to breed this hybrid pińata, leading to another instance of Guide Dang It to figure out how.
Some of the requirements for the Swanana, which include building it a house, setting up a fountain, and giving it an expensive necklace, led to the remark, "The things I have to do for a pig's trophy wife."
Related to World of Darkness's aversion to this trope, people in The Matrix Online have roleplayed Exiles which were a mess of hybridization, including a part vampire, part succubus, part Valkyrie mongrel. Might be justified since it's all code in a virtual world.
Half-Ogres from Arcanum: Of Steamworks & Magick Obscura, like the Top 10 example above, plays the size differences between the two races in a rather dark light... If the female's the human, at any rate. The pre-created Half-Ogre player character is described as the offspring of a human male and an ogress with 'exotic tastes'.
Speaking of exotic tastes, there's a brothel in the game which the player can visit. If you turn down the normal offerings, you can be introduced to Bella. A sheep.
The Warcraft 'verse has Malorne the stag god falling in love with Elune, the night elven moon goddess. Their offspring Cenarius, a stag/elf demigod, was then raised by Ysera the dragon. Cenarius' son Zaetar then fell in love with the earth elemental princess Theradras, which led to the birth of the brutish centaur race.
In Baldur's Gate II: Throne of Bhaal, the god Bhaal is revealed to have had children with everything from chinchillas to dragons and giants in his attempt to cheat death. This ability seems to have been passed down to his offspring; his son Yaga-Shura, a fire giant, tries have a child with a human woman. Bear in mind that fire giants are 12 ft. tall and around 7000 lbs. A player character who isn't a dwarf (as no one romances them) can bear children with elves. Albeit, gnomes and half-orcs (with the official patch) are stuck to Aerie and Viconia, respectively and exclusively. And Viconia wont dally with an elf unlike the other potential romances.
The Asari in Mass Effect, are a humanlike race which can mate with any species and produce viable offspring. This is gotten around by intercourse not being strictly necessary, that the asari and their partner temporarily merge the bio-electricity of their nervous systems and the asari uses the effect of that to randomize a parthenogenic(self-generated) offspring. One asari mentions a past relationship with an Elcor, an alien race that can be described as an intelligent flat-faced hippopotamus.
Played for laughs after Grunt's loyalty mission if you kill the thresher maw. EDI mentions that the feat has sprouted several breeding requests for Grunt, and one for Shepard (which happens regardless of the player's gender). Bear in mind that everybody on that planet is, like Grunt, a Krogan. Your average Krogan looks like this◊. There are also at least two confirmed Asari who have had children with krogan.
In 3, Liara's father (also Asari) had a child with a hanar, a jellyfish like alien. During Blasto, the titular hanar gets some action with an elcor.
Also, a FemShep who has romanced Garrus since Mass Effect 2 can get a dialogue scene near the end in which he mentions wanting to find out "what a turian-human baby looks like." This is the only one that would be according to the game world, impossible, as cross-breeding by different genomes can't happen, and even if it could, turians have Mirror Chemistry and cannot even digest human food.
The (thankfully) fandom-only Crack Pairing of Shepard and Harbinger would also qualify. Shepard is an ordinary human; Harbinger is the first Reaper, and thus is a cyborg Eldritch Abomination that resembles a cuttlefish/crab hybrid the size of a capital ship.
God of War Cronos is a giant big enough to strap an entire building to. God of War 2 shows Rhea as the size of an normal human. Ouch
Still both Chronos and Rhea were reigning Titans/Gods prior to Zeus' times, the game doesn't go far as to say every God/Titan can attain human form and change in size at will, but assuming it follows some aspects quite close to old Greek Mythology texts, Chronos might have had a humanoid form to consummate with Rhea, the same as Rhea might have had a giant form to pack.
Mortal Kombat gives us the Shokan, a race of half-human/half-dragon hybrids.
In the Dragon Age universe, male dragons are wingless and are about the size of a bull. Females, on the other hand, can grow as long as a hundred feet.
8-Bit Theater recently had a "Hot Monster on Red Mage action" with the result, that Red Mage himself was turned into the monster's offspring. The monster, of course, was a lot taller than RM, so that it first looked more like it was trying to squeeze him, rather than to rape him. It was explained by the monster having a third gender to "impregnate" (or rather, transform) other species.
And the less said about the Hot Witch on Dragon-God-King Action that occurred earlier, the better. Notable for horrifying the protagonists, individuals who are most commonly horrifying others with their actions.
Lich, a animated skeleton, has an apparently human wife and his son Vilbert is a vampire. This is eventually called into question and it's mentioned it involved Mind Control at some point.
Averted in a couple of ways in 21st Century Fox with minor character Veronica, who is a vampire bat. It's stated she was in an internet relationship with Cecil, a giraffe, before the beginning of the series. She explains a few times that why a more physical relationship wouldn't be feasible. Later in the comic she gets in a relationship with another minor character, a mouse, and they discuss children opportunities... adoption or getting the father's genes transferred gene by gene to the mother's species.
Chainmail Bikini (now dead) had the Munchkin character Josh created that was one-third human, one-third Drow and one-third Ogre. The other players note that this is physically impossible, which Josh himself doesn't care about. So page #10 is called "Three's Company" and the last panel is a hilariously dubious image of how it'd "work".
Lampshaded in Dan and Mab's Furry Adventures in an exposition strip which mentions a dragon and an anthro-canine who got married and have two children. The author vociferously refuses to answer the inevitable question, though there's an obvious answer given that the one known dragon in the series, Pyroduck, has been passing himself as a humanoid being for most of the series.
The same kind of explanation is used for half-dragons in Drowtales: The Moonless Age , and various Tabletop Games settings.
Also in Dan and Mab's Furry Adventures , a character in the story is a Kangaroo Rat, and has several half-Kangaroo Rat sisters. The "half", however, is taken both ways, as his sisters are all Kangaroos. Their parents are a Kangaroo Rat and Kangaroo (see Marshmallow Hell for details).
This strip explains that the children of Taur and Biped couples will always take after the mother. Apparently it's due to Amber's Fridge Horror considering how painful it would be for a biped to give birth to a taur.
In Jack, almost every character is an anthro, so crossbreeding is just expected to happen. Oddly, though, it seems not only mammals, but also amphibians, reptiles and insect anthros can crossbreed freely, and the parents features somewhat scramble in the offspring. The obvious result is that few of the "mortal" characters are totally "purebreed".
The "Case Of The Travelling Corpse" points out that most species prefer to breed/interact within their own species like the killer. Still, crossbreed families are pretty normal. The child of a mammal and an insect usually ends up looking cute, green and mostly non-insect, for example.
Given the backstory, this becomes more plausible as all the anthro races were deliberately engineered by humans some time in the past, and are probably human inside with cosmetic changes on the outside.
In Kevin & Kell, it seems that even being of the same taxonomic order or class is not necessary for successful cross-species matings. The fox/wolf cross (Rudy) almost seems ordinary when seen with the rabbit/wolf cross (Coney), the wolf/sheep cross (Corrie), the fennec fox/formerly human rabbit cross (Francis), or the tortoise/weasel cross (not named in the strip).
Last Res0rt gets in on it too; the Celeste apparently consist of nothing BUT Hybrid Monster people who breed with all the other species within the comic to make more hybrids.
And then they add WINGS on top of all that.
Averted in Tally Road- after several sexual exploits that are plainly cross-species, the first time any sex with like-species individuals occurs, the guy's seen putting on a condom. Apparently cross-species pairings are infertile.
Averted to a degree in the Chip 'n Dale Rescue Rangers fancomic, Of Mice And Mayhem. During the prologue, Chip acknowledges his feelings for Gadget, but refuses to act on them, because he believes she will one day want to have children, which wouldn't be an option for them since he's a chipmunk and she's a mouse. This is later worked around, as a previous gene splice between Dale and Gadget left Gadget the ability to mate with chipmunks.
One The Order of the Stick comic showed the inherent Squick of family life as a half-orc, the joke being that, in D&D, half-orcs are considered a little bit squicky because they're implied to usually be the result of rape, while in the comic, the kid is squicked because her parents are sickeningly, mushily in love.
They also contemplated the origin of the legendary Owlbear. When Elan suggested that an owl and a bear mated, Belkar expressed hope that the owl was the male in the relationship, as otherwise certain problems would surely arise.
#721 reveals Enor the bounty hunter to be a hybrid of a half-ogre and a dragon. As in, half dragon, one quarter human, and one quarter ogre.
The Ancient Black Dragon is related to at least three half-dragons, one of which seems to be a half-dragon centaur.
One of the strips made for Dragon magazine features a vampiric half-dragon half-troll lycanthropic fiendish snail.
Snail: "Tremble at my illogical glory!"
Yet Another Fantasy Gamer Comic has one instance where the lonely minotaur character decides to stay and live with the lonely gynosphinx character ten times his size. In his own words, "With magic, anything is possible." Though this was less about mating and more about companionship (and the Sphinx's gazongas being big enough that the minotaur could fit his whole body between them). Eventually the question is answered: sphinxes know magic, and she turns one of them into the other's species when they're feeling... affectionate.
And Gren (a goblin) and Bob (a Beholder), how does that even work? I don't wanna know
A sketch on the site shows their hypothetical offspring from a scrapped storyline wherein Gren would have a nightmare about her future children. It could charitably be described as Ugly Cute.
Sabrina Online has this in spades. Sabrina's boss is a skunk with stripes because her grandfather was a white tiger. Thomas is a part wolf, part fox hybrid. And when Amy becomes pregnant with his child...
Amy: Back in prehistoric times, when we were little more than animals, a squirrel like me would only be prey to a wolf like you. But today, we're two different species, but we're also a couple, and I'm carrying our child. Kind of interesting, zoologically speaking.
Thomas: Zoologically speaking, shouldn't this also be impossible?
Coyote: What an interesting first union that must have been!
The World of Warcraft fancomic Druids features a male Tauren and a female Worgen couple. And if that's too much there's one arc where she gets raped by a dragon.
In Space Trawler, Dimitri is basically seducing his way through the galaxy, hitting on and usually sleeping with basically anything female, sapient, and consenting who can physically mate with a human. We're not talking Green-Skinned Space Babes either. We're talking a woman who looks like a bright pink cross between an anteater and a giraffe, a green egg-shaped insect alien with antennae, an orange person with a worm-shaped head and gills (although also with a bangin', suspiciously humanoid body in a form-fitting jumpsuit), and a mauve creature with a profusion of long thin prehensile tentacles on the bottom and a tall, glowing cylindrical appendage on top. Link. Among others. Many others.
Choan: What about the furry-faced one?
Nogg: Him? Dimitri will sleep with anything that has a sexual compatibility index over 50%.
Choan: Is Nogg correct, Dimitri? You and I have a 74% compatibility.
Dimitri: A beauty like you? How could I say no?
Choan: I'll see you after dinner in my quarters then.
TwoKinds: Double Subverted. There are three civilized races in the setting; Humans, Keidran, and Basitin. As far as anyone knows, breeding between the races is impossible. Until Flora, the human main character's keidran wife, somehow becomes pregnant with his child. It's implied this is because of divine intervention, with one of the powers-that-be allowing it to happen instead of preventing it as has been done up to this point.
Also happened with Raine's parents. Her mother was a templar, her father was a Keidran who had mastered the ability to perfectly transform himself into a human. They had sex and her mother got pregnant, and was very surprised to deliver a Keidran-looking child. Raine inherited her father's ability, but can't control it, and will revert to her Keidran form without magic suppressing items.
The series of artwork (often NSFW) about adventurers by Fredrik K.T. Andersson (author of Pawn) includes a character best described as "Bard who knocks up every critter in creation". And is so much surprised by the results one may suspect he was drunk half-blind during those encounters. This one is safe-for-work, if potentially hurtful for a brain. Of all living beings he had troubles only with elves. Also, there's "Dragon and Succubus". Speaking of which—
Elf Ranger: And what part of "naked chick standing on top of a dead dragon" didn't say major demon to you?!
Human Bard: (lifted off the ground by a happy embrace of "chick" with hooves and spiked tail) uhm... the "naked chick" bit... ?
When Little One in Tales From My D&D Campaign has to explain that his mother was a dragon, one of the other players brings up this trope. However, Little One explains that dragons can assume human form if they so desire.
The Simpsons. One Tall Tales episode has Marge falling in love with a Paul Bunyan version of Homer. When Homer questions her about finally consummating their love, Marge states that she'll do it after she finishes taking a few more yoga classes.
And for Halloween Episodes in one Abraham Simpson (AKA Grandpa) Was doing a "King Kong" Parody, with Marge as the woman and Homer as King Kong. They got married at the end...I don't want to even THINK about them consummating it.
She'll be getting some hot monkey love, that's for sure.
Ben 10: Alien Force introduces the Half-Human Hybrid Plumber kids; all of them being, well, alien hybrids. One of the first ones seen is half Pyronite, half human. Pyronites are beings made of magma, are constantly on fire, and live on a sun. The only mix that might be weirder would be a half Galvan (Greymatter), what with a Galvan being a six-inch tall, bug-eyed, grey alien...
Though the weirdest has to be Gwen. An energy being? How'd that work? One can only guess it was halfway between the standard fashion and magical creation.
Gwen is one relative removed from that lineage. Her father is the son of Max Tennyson and Verdona, her energy-being grandmother. As Verdona demonstrates, she can outright warp reality on a whim. Creating human organs was probably simple. The "spark", as she called it, carried on in her offspring from that point.
It gets weirder when you realise that said "spark" won't necceserily 'take'; Besides Verdona, Gwen is the only member of the family with Andonite powers, the rest (including Ben) being merely carriers. Gwen's powers, in essence, are the direct result of an STD (or rather, virus)...
Not only that, but Ben HSOWA's the entire High Breed race at one point, injecting DNA from all the other species of the universe into the High Breed.
It should be noted that interbreeding is primarily a human-on-alien thing, not an alien-on-alien thing. Apparently, it's one of humanity's greatest assets that it can take the best traits of other species and add them to its own gene pool.
CatDog comes close: A male frog and a sasquatch are the protagonists' parents... by adoption.
Oh but it does have a answer... Irwin's grandfather is Dracula which makes him a Dhampyr and since it makes him a half-monster and mummies are monsters then that explains the compatibility, of course we don't know this until "Dracula Must Die!"
More than one website has described Irwin as "1/4 vampire, 1/2 mummy, 22/7ths nerd".
In the pilot for Squidbillies, Early Cuyler had romances with his morbidly obese human lover, Krystal, and while he was in prison, she was pregnant with Rusty, who, shortly after his birth, was abandoned in an empty chicken bucket to be raised by Early's sister Lil. 15 years later, Rusty finds Early working on a chain gang and they reunite.
And years later from that, half-land squid, half-human Rusty and his all human girlfriend Tammi have an apparently all human child that she names Macho-man Randy Cuyler.
A series of Tex Avery cartoons asserted that the car, home and farm "of tomorrow" would include crossbreeds of both living beings and inanimate objects— corn crossed with Mexican jumping beans to make it hop into your mouth, etc.
Geldhemoor: I am a hunkeycorn — half hummingbird, half donkey, half unicorn. Gandhi: A hummingbird and a donkey doing it? I hope your mom wasn't the hummingbird.
Not to mention that Geldhemoor later offered to lay Gandhi. Thrice.
The Cartoon Network original movie Firebreather has the main character Duncan, whose mother is a human and father is a massive Kaiju. It's Lampshaded in one scene when his mother tries to explain how its possible, only for him to refuse to listen.
In the Ren and Stimpy Adult Party Cartoon episode "Altruists" Stimpy puts on a female duck costume to make the guard duck fall in love with him, when they start making out Stimpy lays eggs with contain half cat and half duck creatures.
Carter thought Brian knocked up his prized greyhound. When the puppies were born, they looked amazingly like Ted Turner...
Brian did father a perfectly normal human child with Tracy.
In an episode of Spider-Man and His Amazing Friends, a frost giantess falls in love with Iceman and tries to make him marry her. She doesn't see anything unusual about this, but he's terrified.
Iceman: I can't marry you! You'll probably step on me!
There's a trio of Mons-based web roleplaying games, unofficially known as the Hidden Crossroads, that use this trope. The first such site alows for any two creatures to breed via a special item; the results are Mix-and-Match Critters. The other two sites have several different types of Mons that can only be obtained via breeding, but they're all variants on the same species.
Pretty much all Half Human Hybrids in fiction if you think about it. We're talking about species that share no common ancestor, or at most a common ancestor billions of years back (in a panspermia universe). A human would probably have much more in common biologically with a mushroom than with an alien. Yet somehow you have examples of them mating and producing viable offspring. The mind boggles.
Spock, of course, being the most famous example. Given that two humans can have a problem if they are of blood types, say, A+ & B-, how the heck do beings with copper- and iron-based globin get anywhere? Though some material mentions it took some technical intervention.
This is mostly justified in that in one episode of TNG, the crew finds evidence that all the factions, including klingons, and romulans, were tampered with by an ancient race with traits of all races. They found planets with evolving life and decided to step in, and force their evolution in their image.
It's also further touched on directly in an episode of Star Trek: Deep Space Nine. When Dax (a Trill) announces that she and Worf (a Klingon) are going to try to have a baby, Bashir, the station's medical officer, looks crestfallen for two reasons: one, he knows Dax is truly out of his reach forevernote not quite, actually, but that's a different trope, and two, he's apparently going to be the one who has to make Trill and Klingon genetics play nicely together. He even warns Dax to not get her hopes too high, because it'll apparently be a real challenge.
"Then why is her belly not distended with a squirming brood of grubspawn?"
"Because I'm not from this planet! Our biochemistry is totally different! He'd have more chance trying to impregnate a native plant than he would me!"
"And even that would be impossible! I used to do it with fruit all the time and nothing came of it!"
The online Flash incarnation of You Don't Know Jack had Nate the Intern leaving the show to marry Tiny the Elephant at the end ofEpisode 60. No known offspring resulted, though.
Cookie: Are you registered anywhere?
Nate: Yeah, Home Depot. We could really use a ladder.
On the Neopets website, there's even a book that lampshades the oddity of Neopian family lines, such as a Skeith and a Zafara having a Lupe, an Ixi, and a Gelert as their offspring.
NeoQuest II has this with pretty much every NPC that has children. For example, in a village in Chapter 3, one family is made up of an Acara (a cat/goat hybrid) father and a Wocky (fox) mother, who have children who are a Cybunny (rabbit) and an Uni (unicorn).
The Brobdingnagian Bards song Do Virgins Taste Better? wonders why dragons prefer kidnapping virgins to any other kind of person.
"Dragons and virgins. Dragons. And virgins. The mechanics alone boggles the mind."
"I crossbred a hedgehog with an earthworm. The result was: One yard of barbed wire!"
"Interesting. But I managed to cross a pig with a letterbox. The result: A piggybank!"
There is a joke about a man who crossed a cockroach with a watermelon - now, there is no bothering with getting the seeds out.
Then there's the guy who crossed a Blue Tit with an enormous pear tree, and was very disappointed to get an enormous pair of blue trees.
The wizards on Discworld never got very far in figuring out genetics, as their initial experiments in crossing garden peas and fruit flies only resulted in a green bean thing that buzzed.
It's possible, though it doesn't happen in the wild due to different ranges, for a Reticulated Python (the longest snake in the world) to breed with a Ball Python (a much smaller python, usually reaching four feet in length). Generally anyone trying to do this will use a large male ball python and a younger (therefore smaller) female reticulated python, or one of the dwarf species (still eight to nine feet of snake), for obvious reasons.
In one episode of QI (season D, episode 3) about dogs, all four panelists were given two canine plushies and asked by host Stephen Fry to show how dogs mate. Some panelists had plushies that were wildly different in size from each other. The discussion mentioned that (in theory at least) a chihuahua and a great dane could breed. Alan Davies then quipped, "They would need either a ladder or a ditch." That line then became a Running Gag throughout the remainder of the episode.
In Bill Cosby's old "Seattle" routine, he describes the Seattle Zoo's attempt to induce their old male gorilla to mate. As a last resort, they shoot him with an aphrodisiac-filled dart, which the ape pulls out and throws away when it does nothing for him. Unfortunately, it strikes a hippo.
Bill: "And the hippo went wild! I mean, everything....birds, trees, grass, garbage cans. He was all over the place. As a matter of fact, they have some of the weirdest-looking animals out in that zoo now....they have a giraffe with a hippo's head and his neck can't hold the head up!"
There is a weird, almost universally-rejected scientific hypothesis which proposes that caterpillars exist as a result of early butterfly ancestors interbreeding with velvet worms.