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Hybrid-Overkill Avoidance

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This has its drawbacks.

"For years, we've been trying to combine the bloodlines [vampire and werewolf]. And for years, we've failed. It was useless. Even at the cellular level, our species seemed destined to destroy each other."
Singe, Underworld (2003)

Some people like a Ninja Pirate Zombie Robot, which is why making a Hybrid Monster that combines two fantastic creatures into one, like a cyborg-centaur or a demon-elf, is popular in fiction. However, like most good things, it can be a bit overdone.

This is especially true when an author wants to conserve as much Willing Suspension of Disbelief as possible; believe it or not, readers might have trouble swallowing a half sunlight elemental / half vampire.

In a superhero setting, which is often a Fantasy Kitchen Sink, the trope expands to include 'super-origins' as well. A character's powers, however diverse, need a single unifying theme. Logically, if aliens and Functional Magic are real, there's no reason magic would be restricted to the one planet Earth and there must be alien magicians somewhere in the universe, but they won't appear as main characters. Undead who are bitten by radioactive hamsters don't manifest additional hamster-related powers: they just eat the hamster.

In a game setting, this trope is used to avoid the presence of Ninja Zombie Pirate Robot throwing Competitive Balance right out the window when you can, within the rules, get any power listed on any species' charts with limited or no Necessary Drawbacks. It's essentially a way for the designers or Game masters to avoid someone making an overpowered Red Mage. Smart game designers (or ones that have had experience like White Wolf, makers of The World of Darkness) have gone the extra mile to explain why such hybrids can't exist.

Inside the story, this is usually justified (or at least given a decent Hand Wave) by having one supernatural/technological/biological "monster" or race be naturally immune (or violently allergic) to being hybridized with another. For example, a character who's been changed into a werewolf can't be mutated with The Virus since their Healing Factor protects them from further mutation. Robots won't become ghosts if they don't have a Soul in the setting.note  For whatever reason, in some settings characters can only change into one kind of supernatural critter, or only be one "at a time".

Sometimes, the "immunity" is due to the idea that the character can't be changed from one type of their common category to another, such as zombies and vampires, which are different types of their common category of undead.note  Sometimes the offspring only inherits one of their parent's types, or a few, but not all, of either's traits. Subverting this trope is usually a very big deal, it marks the birth of a powerful and Unique creature that can upset the Status Quo thanks to One Hero, Hold the Weaksauce.

See also Hybrids Are a Crapshoot, where this trope is averted with detrimental results.


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    Anime and Manga 
  • Bleach: Quincies and Hollows are opposite existences to one another, enabling Quincies to utterly destroy Hollows instead of cleansing them like Soul Reapers do. On the flipside, Hollowfication — which involves fusing a Hollow's soul and/or spiritual power with a host's to create a hybrid — empowers Soul Reapers but is extremely toxic to Quincies, with only one known case surviving due to unique circumstances.
  • BNA: Brand New Animal: While different species of Beast Man can procreate with each other, their children always belong to one of the parents' species - hybrids don't exist. It later turns out that different kinds of Beastmen breeding results in offspring that are weaker. The Big Bad is a pure blooded wolf beastman who wants to wipe out all of the beastmen with mixed ancestry because he sees them as inferior beings and not real beastmen.
  • In Tokimeki Tonight, protagonist Ranze's father is a vampire and her mother is a werewolf. She's apparently normal, with no traits of either, until she develops retractable fangs and anytime she bites something with them she turns into that object until she sneezes. Rinze, her five year old brother, is more or less a werewolf.
  • The Dark Queen and I Strike Back:
    • Different kinds of inhumans can interbreed, but the resulting mixed-blood offspring will only show traits of one inhuman type (and will look closer to humans than pureblood inhumans).
    • Glorya (and apparently other Arborian Dryads) is an exception to the general rule. She can produce offspring with traits of other inhumans, though so far these are all shown to be non-sentient.
    • Tsukumo and Sumire are exceptions, but they're the result of experimentation rather than natural birth.
  • Monster Musume confirms that any child of a monster/human pairing is an apparently un-hybridised monster, this being the only thing that allows certain one-gender species to survive. Mia, Papi, and Centoria are all examples.

    Comic Books 
  • Marvel Zombies:
    • The series overall toys with this. The entire premise involves the fact that the zombie virus affects essentially all superheroes, which naturally leads to superhero zombies, as well as zombies based on all manner of other superhero-adjacent entities (such as Morbius becoming a vampire zombie). However, it's also shown that becoming a zombie can sometimes shut down aspects of a hero's powers—for instance, heroes with Healing Factor abilities lose those abilities, since zombies can't heal. The plague also can't affect anything fully robotic.
    • Werewolf by Night gets infected with the zombie virus, but because his biochemistry changes when he transforms the disease remains limited to his human form. So hitting the human zombie with magically created moonlight gives back a healthy (but feral) Wolf Man.
  • In Young All Stars, there's an Axis agent called Sea Wolf, a water-breathing werewolf.
  • Exploited in The New Deadwardians, in which the upper class of post-Victorian England protect themselves from a zombie plague by taking "the cure". What is "the cure"? Why, vampirism.
  • Post-Crisis Superman comics say that Kryptonians couldn't have children with normal humans but could theoretically breed with humans or aliens with similar powers such as Wonder Woman or Maxima.
    • Before the Crisis on Infinite Earths Kryptonians could breed with humans but the child would be half as powerful, with each generation's powers being halved the more they breed with humans.

    Films — Live-Action 

  • The hippogryph was considered a mythological creature by the standards of mythological creatures. Gryphons (lion-eagle hybrids) eat horses, so the idea of a lion-eagle-horse was deemed completely impossible.

  • Zig-Zagged in The Sanguine Chronicles where, like Underworld (2003), being one immunizes you from the other. Marko is, however, a VERY rare aversion.
  • Averted in the Xanth series in a several ways:
    • To begin with, each succesive human generation has a chance of becoming less human and more magical than the last, evolving into all sorts of humanoid things like goblins, dryads, fairies, and metal-people.
    • Any humanoid or human-ish thing can succesfuly hybridize with any other humanoid or human-ish thing.
    • Any two species of any sort who simultaneously drink from a love spring will copulate, and will subsequently issue hybrid progeny. (Horse + human = centaur is the usual example given. Squick.)
The only reason that there are still humans in Xanth at all is that successive waves of immigrants from the mundane world keep coming into Xanth and replenishing the gene pool before it disintegrates.
  • My Vampire Older Sister and Zombie Little Sister: Vampires and zombies are unable to infect each other. There is one occasion where a human is bitten by both simultaneously, but they die (of injury) before either infection can take hold. It's worth noting that the two races also have different means of infection: vampires need to specifically suck out a lethal amount of blood, while zombies can infect with just a bite. As a result, it would probably be difficult for someone to be infected by both, even if it was possible.
  • Done differently in different places in The Lord of the Rings. Elves and humans can reproduce, but their descendants have the choice of whether to be human or elven. For example, Elrond chose to be an elf and remained immortal (despite being given the epithet "half-elven"), while his brother chose to be human and died having lived not much longer than other humans. Arwen, Elrond's daughter, later chose to become human when she married Aragorn, despite having already lived a couple of millennia as an elf.
    • The uruk-hai, on the other hand, are hybrids of orcs and humans, and are bigger and stronger than both while not suffering from weakness to daylight like regular orcs.
  • In one of the Anita Blake novels, a character reacts with surprise when he hears about a vampire who is also a pedophile because it is supposed to be impossible to be more than one kind of monster at a time.
  • In The War Gods the 5 races of man are 5 different human subspecies. While its possible for any two to have a child together, the resulting hybrid usually is infertile.
    • Half-elves are the main exception as a True-Breeding Hybrid, with the Purple Lords trying to make Half-elves recognized as the sixth race. However, if Half-elves have children with a human, the children are purely human. Half-elves can only product half-elf children with elves and half-elves. Enough half dwarves have also existed that some dwarf-blood is common in the Axemen.
    • However, the biggest issue appears to be how the species ties to the magic field. Elves tie into it for immortality (but used to be a Mage Species). Dwarves have stoneworking magic, Hradani get stamina and antimagic, Halfings their dexterity. Only Human and Human-Hradani hybrids can become wizards however.
  • There was a werewolf in The Southern Vampire Mysteries who was bitten by a vampire and lost the ability to transform into a wolf. Sadly given the Fur Against Fang setting, he's hated by both groups.

    Live-Action TV 
  • The "Jefferson Starships" from Supernatural were hybrids of various monsters that have appeared in the series. However, since they were unstable experiments created by Eve, they had all died by the time they were encountered (and named) by Sam and Dean.
  • In The Vampire Diaries this has been imposed on Klaus, who is a werewolf vampire. Because the resulting hybrid would be too powerful, witches cursed him to suppress his werewolf side, preventing him from transforming at the full moon. His goal is to break the curse, allowing him to create his own master race.
    • Furthermore, a witch who becomes a vampire immediately loses his or her connection to nature and the powers along with it. The in-universe explanation is that vampirism is an abomination against the balance of nature, and in any case a vampire is (un)dead anyway. The meta reason is of course that witches are already super-overpowered and giving them the powers of a vampire on top of that would make them untouchable.
  • Vampires in Being Human are unable to feed on and, by extension, turn werewolves because werewolf blood is toxic to them. Werewolves who attack vampires while transformed are more inclined to kill them outright rather than turn them. No explanation has so far been offered as to why vampires and werewolves don't become ghosts, although one ghost has dismissed the idea of werewolf-ghosts as 'ridiculous' without further explanation.
    • There was a werewolf ghost at one point but they immediately crossed over so we don't know if any of the 'wolfiness' carried over to their spirit form or not.
  • In Buffy the Vampire Slayer, the titular Slayer is considered a human monster by some (having been infected with demonic power by the Shadow Men, the first Watchers). In one episode, while Sunnydale is caught inside a boy's psychic nightmares, Buffy is temporarily turned into a vampire, making her a Slayer/vampire hybrid and more than twice as strong as either is shown to be separately. However it's left unsure if this could happen in the "normal" course of events in the Buffyverse, as most vampires would prefer to kill a Slayer than turn her.
    • It's notable that a one-shot episode villain in season 4 who easily beat Buffy was going to be explained away as a vampire/Slayer hybrid, only to be cut for time and pacing.

    Tabletop RPG 
  • The World of Darkness games enforce this trope for balance issues. Hypothetically, though, any supernatural that can be changed back to human can be turned into another type.
    • New World of Darkness:
      • Vampires are dead humans resurrected to unlife by an as yet unexplained but likely magical force. Arcadia will not mutate them because, to borrow a line from Doctor Who, they are facts, in the metaphysical sense: they cannot change. They are stuck the way they are, and nothing (about the twisted nature of the Fae realm - let's just ignore the Ordo Dracul for the purposes of this discussion) will ever change that. They were human; they were not created, whether by man or the God-Machine. They already have powers, so the desperation to take up the vigil never comes to them. While Luna may be mad, she does not bestow her gifts upon the undead, even if they were wolf-blooded in life. Similarly, geists bargain with the newly dead they can restore to life, rather than the undead. The Rite of Return was last enacted over six thousand years ago, and there's no one alive who knows how to perform it - not to mention the question of whether it would work on the undead. Lastly, not having the spark of true human life anymore, they can't awaken to true magic, and have lost the deep connection to the Primordial Dream that would allow a primal nightmare to replace their soul.
      • Likewise the reverse is true. Only an ordinary mortal human with a human soul can become a Vampire. Even attempting to feed off a supernatural creature, a necessity for the Embrace, will most likely lead to the Vampire getting torn to pieces, magically fried to a cinder, or worse. Like being more prone to raging and giving into the Beast (Werewolf blood), having a bad acid trip (Fey or Mage blood) or other effects.
      • Werewolves are... well, it depends on your interpretation of the "scriptures," really, but the fact is they are physical spirits. They don't die; they ethereally recycle, so to speak. This means they can't be embraced as vampires, nor can they make the bargain to become geists. They are natural occurances, not created beings like Prometheans or demons. They are not human, so they can't become mages, nor can they be altered by a spirit realm like Arcadia, which their supernatural "biology" is already adjusted to (to say nothing of their psychologies, which may be less resilient). As mentioned previously, the Rite of Return is long forgotten, so they can't be transformed into a mummy. And again, no human desperation equals no vigil.
      • Wolf-blooded, however, are a rare exception to this trope. The book explicitly states that a wolf-blood can be turned into other sorts of supernatural, and will retain his Tell and associated abilities when he does so.
      • Vampires, werewolves, Prometheans, changelings, mummies, demons, Beasts and ghosts can't Awaken as mages because they're not human and/or not alive. Mages who become vampires or ghosts lose their mage-ness in the process.
      • Technically, you can make a Promethean out of anything's corpse (if it wasn't a straight-up human, though, it's kind of tricky). But that's exactly what you get — a Promethean. Not a Promethean-werewolf, not a Promethean-mage, not a Promethean-changeling — a Promethean. None of the other powers carry over, because they all went away the first time the body died.
      • Prometheans who complete the Pilgrimage lose nearly all Promethean abilities, essentially reverting to ordinary humans. While this means they can theoretically become vampires or mages, the books advise that you only do this for a very good reason — and the Rule of Cool doesn't qualify. This is quite a good way to add on a bittersweet ending, a Promethean becomes a human again? Oh, but wait...he's cursed to live among the undead for the rest of his days. It's the sort of thing that should only really be used for the most grimdark of chronicles.
      • Also theoretically averted in a sense by any supernaturals who could turn into Hunters and become members of a Conspiracy, where they could then gain Endowments. Of course, if the other Hunters found out who they were, in many groups they'd be on fire in seconds. This only works if A: the DM accepts the letter of the rules and not the spirit invoked by the flavor-and-backstory text, or B: the character has a very short conscription into becoming a Hunter and a somewhat-to-very long transformation into a supernatural which reached the point of no return before the full-fledged-Hunter immunities kicked in.
      • Somewhat more averted with the endowments of Task Force Valkyrie: their endowments require a special chip implanted in their agents to function, so if the chip was taken out and implanted in another suitable creature, presumably they could make use of some of their technology as well. And some Endowments, like specially created bullets, don't even need the chip to be used.
      • The above aversion also applies to Aegis Kai Doru's Relics. You only need to know the correct way to activate relics to use them, so anyone, supernatural included, could potentially use them.
      • Fan gameline Leviathan: The Tempest has a soft version of this. It is possible, and even common, to have a Hybrid who draws their inhuman heritage from multiple Strains of Leviathan, but there's no advantage to doing so. In fact, Lahmassu (Hybrids who are descended from only one Strain) have certain advantages over "mutt" hybrids: they get some minor bonuses based on their ancestral Strain and have to take fewer Genetic Conditions.
    • The Old World of Darkness has similar rules to the above to prevent gratuitous crossover, and to encourage players to make their characters distinctive through good character development and not just (to quote one of the designers) "having a grab bag of powers no one else has":
      • Only humans have avatars, so only humans can Awaken to become Mages. Becoming undead of any kind gets rid of the avatar, nixing that option. Shapeshifters were born as shapeshifters, Umbral spirits in fleshly form, even if they resemble humans or animals at birth, so they lack avatars. When they die they go to a different kind of afterlife than human dead, so they can't become wraiths, zombies, or Kindred of the East.
      • Shapeshifters can go to the Dark Umbra if they're corruption-tainted and severely unlucky...but they'll be functionally no different from any other human wraith.
      • Similarly, only humans are selected for the imbuing, since their entire purpose is to stand on humanity's behalf against the forces of the supernatural. Becoming imbued grants immunity from becoming a supernatural, save in one case: extremist imbued who have given themselves over to the hunt can become servants to demons. By breaking the extremist's will, the demon can take over their body, but the process destroys the extremist's soul, and the newly embodied demon retains none of the extremist's powers save those they themselves granted.
      • Within Vampire: The Masquerade exists rules that prevent Kindred from being a hybrid of two or more vampire clans. Should more than one kind of vampire's blood be used in an embrace attempt, the blood with the lowest generation, highest age, and greatest potency will overwrite the rest.
      • One exception is a vampire-werewolf hybrid "abomination," extremely tricky but possible. Werewolves are violently allergic to vampire blood so if you try to 'embrace' one, he gets a roll to see if he died peacefully or in horrible pain. Unless they're out of all Willpower, they get to die automatically. A hybrid is created only if you botch that roll. A hybrid does have access to all the powers of both but has to watch the Karma Meter very carefully - from a spiritual point of view, werewolves and vampires are pretty much opposites (one being a nature spirit that just happens to have flesh while the other is a dead shell with barely any spiritual presence) so straining too far will be detrimental to all spirit-related powers. Their Gnosis now functions like a normal vampire's Humanity and goes down from actions unbecoming of a Garou. They retain their old Gifts but can no longer learn any new ones except from corruption spirits. And if their Gnosis runs out, they go into a mindless rage until someone or something inevitably puts them down. That's if they get to that point, of course - plenty of both vampires and werewolves will put them down just for existing, especially the latter, and they're also not unlikely to be depressed enough about their new nature to do themselves in, either directly or Suicide by Cop.
      • Several other Changing Breeds either can't be embraced, or make the embracer wish he'd never tried. Kitsune (were-foxes) explode in fire if embraced as kind of a Take That! to players' obsession with making abominations. Corax (were-ravens) die come dawn... even if they're never exposed to sunlight. Mokolé (were-lizards/crocodiles) enter a murderous rage, assume their most powerful form, start rampaging, and then die at dawn. Rokea (were-sharks) survive, but lose most of their personality and become relentless vampire-eating horrors. Bastet (were-cats) immediately start losing their Gnosis stat, which cripples their supernatural abilities and erodes their ability to mentally function as anything but near-mindless blood-suckers. Ratkin (were-rats) are embraced with no less trouble than Garou, but then start to decay like a normal corpse.
      • Faerie-blooded, including changelings, can occasionally be embraced, but it robs them of any fae-related powers or memories they may have had. However, the Curse of Caine is not untouched by mixing with the blood of the fae; the new vampire becomes one of the Maeghar, gaining access to the Disciplines of Mytherceria or Necromancy, but also gaining a physical mark identifying their fae nature, a vulnerability to cold iron, and a psychological aversion to drinking directly from mortals, requiring a container instead. (Interestingly, this seems to have mutated over time in-universe; in the Dark Ages setting, they didn't have Necromancy or the psychological aversion to drinking from mortals).
      • Another exception is fomori, the fusion of a spirit of corruption with a material host. The most powerful of such spirits can pull it off on a supernatural host, specifically vampires, werewolves and most shifters, mages, and changelings who've forgotten what they are. Long, long ago, the vampire Set spawned the dread Bane Mummies through corrupt magic, and found they had their own agenda; fortunately for everyone else, Set wisely decided not to try again, and no one else seems capable of it either. Most every other major supernatural is immune, including two of the Changing Breeds: the Corax were-ravens (thanks to their unique creation ritual) and the Nagah were-snakes (since they're a spiritual blind spot). And while being a fomor may offer the occasional benefit, they're far, far outweighed by the downsides of being possessed by an evil spirit.
      • There's at least one example in canon of a Werewolf becoming a Mummy after death, the Silent Strider Wepauwet. After the Striders were cursed to be cut off from their ancestor-spirits, Wepauwet sought immortality so he might serve as a living repository of the Striders' history. Unfortunately, he learned the Rite of Return didn't have the same effect on Garou it did on mortals - he only got to return from death once, and if he died again he would be cursed to wander the Umbra as a fleshless spirit, denied both his living people and his Umbral Tribal Homeland. He presently resides in the Strider Tribal Homeland, where he serves as a link between the Striders and their lost ancestors, and has learned how to enable a rare few mortal Striders to circumvent the curse and call upon their ancestors.
      • Also averted by the infamous Samuel Haight who was a ghoul-werewolf-true mage. Until he died, became a ghost, and was soulforged into an ashtray. It's worth noting that the ashtray fate came about when people asked White Wolf where Sam Haight was in the Wraith line, after he'd been worked into all the others via hybridization. Staff response was to retort that he'd been soulforged into an ashtray to keep him from being a major player in the line. This in turn led to fans creating missions for Orpheus to incorporate the ashtray. Entries can be found on CWAL.
  • Some templates in the 3rd Edition Dungeons & Dragons game can only be applied to specified creature types, or to creatures with specified traits. This restricts some abuses, but an imaginative DM can still do some crazy things.
    • Only living things can become undead, so no Ninja Pirate Zombie Robot (flesh golems are constructs, not undead).
    • Constructs cannot breed, and thus cannot be half-dragons or any other inherited type.
    • Undead are immune to disease, and thus cannot become lycanthropes.
    • Undead flesh may not retain all the natural abilities it had in life, and skeletons have no flesh at all.
    • Lycanthropes and vampires can only convert humanoids, not animals, constructs, abberations, fey or any variety of dragon (draconic or mind flayer vampires use a different template).
    • Lycanthropes can become undead, but most undead types would lose the ability to shapeshift (though vampires do not). It is therefore possible to create a vampire werewolf, but only if you apply the templates in the right order.
      • Namely, a living werewolf can be turned into a vampire, but a vampire cannot contract lycanthropy due to the undead immunity to disease.
    • Undead that take class levels would almost certainly be prohibited from taking levels in Druid, and even if they could they couldn't use the Wild Shape ability (except vampires again). Besides, Druids in Wild Shape lose any physical attributes of their base form for the duration.
    • Dragons, celestials, and fiends can breed with just about anything, but only if it's living, and the results of such breeding may not convert well into useful undead.
    • It is possible to graft construct parts onto a living creature to make a half-golem, but the result risks becoming a construct (there are saves involved -- succeed and you keep your original type and alignment, fail...) and thus no longer counts as living, which restricts the ability to apply other templates, and they do not breed true, if they can breed at all.
      • The other way of grafting construct parts onto a living creature (using a subsystem based on items instead of templates) did not have any type-changing involved, but was written in a way that implied it only worked on a living creature, had rules against having too many, and had rules against combining different types of grafts (so you could have a couple of construct grafts, but not a construct graft and a plant graft).
      • This makes possible the Half-black-dragon, half-iron-golem troll, which is immune to damn near everything, but would require a black dragon (acid-breathing and acid-immune) to breed with a troll (vulnerable only to fire and acid), and the offspring to be converted to a half-golem at great difficulty and expense, probably against its will. Neither the victim nor its parents are likely to be pleased.
      • Taking the above even further is The Emerald Legion, an attempt at a magical Super-Soldier which (among other things) also makes the troll a quasi-Dhampyr and has it bitten by multiple lycanthropes of different species.
    • For player characters, the main mitigator is Level Adjustment, a virtual inflation of the character's effective level imposed by most beneficial templates. For example, a half-dragon has an effective level adjustment of +3. A 1st level half-dragon character is thus theoretically as powerful as a 4th level character, and thus not legally playable in a group starting out at any level below 4th (and s/he would start out at only 1st level in one that was). The level adjustments of all templates on a character are additive. Level Adjustment also makes it more difficult for a character grow stronger, as its Effective Character Level (Level Adjustment plus any class levels) is what determines experience gains and the amount of experience needed to level up. As a result, Level Adjustment is actually an even bigger mitigating factor at higher levels, and it can easily get to the point where the bonuses conferred by the template are outweighed by the drawback of slower EXP gain.
    • All of which leads to a joke in one of The Order of the Stick comics for Dragon magazine (paper version) about a vampiric half-dragon, half-troll, lycanthropic, fiendish snail. The snail had a challenge rating of 14 (meaning it would be capable of challenging four level 14 characters by itself), despite being small enough to step on. "Tremble at my illogical glory!" indeed.
      • In the main webcomic, a vampire cleric is later introduced who mentions that being a vampire (with a whopping +8 level adjustment, and another +1 adjustment as a lizardfolk) makes it difficult for him to find level-appropriate opponents and thus he hasn't gained any relevant amount of EXP in years. This ends up being relevant to the plot; the gods of the setting need high-level clerics to participate in certain events, but some of the evil gods have only undead clergy which are effectively prevented from leveling (turning a high-level cleric is one obvious solution, but high level clerics are the best fighters against undead).
    • The Eberron setting has a significant number of rules standing in the way of doing anything too unusual with dragonmarks, heritable magical symbols that confer aptitude for certain skills and have been combined with certain magical items and legal effects to give the dragonmarked houses near-monopolistic power in the Khorvairian economy. The genetic lines of descent only reach so far, meaning that highly divergent subraces (drow, duergar, deep gnomes etc) don't manifest it. Becoming something else will negate your dragonmark, so a dragonmark heir who is turned into a kind of undead will lose that power (much to the frustration of Erandis d'Vol, whose incredibly powerful Apex Mark of Death has been reduced to just a permanent tattoo with her lichdom). Nor can you have two dragonmarks, with the child of two dragonmarked heirs being more likely to develop a unique and potentially dangerous aberrant dragonmark than either individual mark. Heritability across playable race boundaries is a tricky one: only half-elves (who breed true in this setting) can bear two of the marks, but the half-elven child of a marked human or elf, or a changeling born from a liaison between a marked member of any species and a changeling, can't inherit a dragonmark from either side of the family...but both half-orcs and humans can inherit the Mark of Finding. There has also been at least one documented half-dragon inheriting a mark - indeed, an extraordinarily powerful one - but that was part of a deliberate breeding experiment with the goal of creating someone capable of bearing that mark, may not work similarly in the case of individual consensual encounters with dragons, and was considered such a problem that the family line that attempted it was exterminated to such a degree that their mark no longer exists.
  • Exalted has rules to prevent most forms of supernatural mix-and-match. Not only were most non-human races genocided in the Primordial War, but all mortal races have distinctly different souls. Exaltation only works on humans. The main non-human races, Dragon Kings and Mountain Folk, reincarnate upon death, so they can't become ghosts either. On the other hand, Exalted has a remarkably lax definition of "human," so most Wyld Mutants and half-animal Beastmen count and can exalt. God-blooded (people with one human parent and one parent who's a god, elemental, demon, fae, exalt, or ghost) are likewise human enough to exalt, but half-exalts become normal exalted with no special traits, and the other kinds gain new powers painfully slowly after exalting.
    • Digging down into "Exaltation only works on humans", this was primarily intended to emulate something like mistletoe killing Baldr in Norse mythology; the Primordials didn't think to protect themselves against something as insignificant as humanity, and the gods took advantage, exalting humans to give them the power they'd need to take the Primordials on. Third edition establishes there was at least one nonhuman species that got its own exalted, the now-extinct Spoken, demonstrating that humanity wasn't unique, but happened to be in the right position at the right time to be the gods' primary choice.
  • Warhammer has virtually no "hybrid" types (although there were a few in its very earliest editions, which have been scrupulously removed). Elves, Dwarfs, Humans, Ogres, Skaven etc. are separate species and can no more breed with one another than a man can with a horse (and Centaurs are a completely different species again). The Orc races do not reproduce sexually. Daemons do not breed at all. Vampires all began as humans (their curse derives exclusively from human blood) and so on. Indeed, the prevalence of hybrid types in many other famous fantasy universes (especially D&D) is what caused the designers of Warhammer to eschew them entirely. The closest Warhammer gets anymore is certain one-off Chaos mutants, which are simply members of one species with an aesthetic resemblance to another (and this is not dwelt upon anymore, precisely because it might dilute the strong racial archetypes that are being maintained).
    • Skaven Rat-Ogres are another possible unnatural version - being crafted from parts of Ogres and Skaven by the frankenstein-esque mad scientists of Clan Moulder. They behave as a completely new (and almost entirely mindless) creature, however.
    • The basic, mindless undead can be created from any corpse, if the battlegame's Regiments of Renown are to be considered a canon source — but they're just corpses animated by necromancy and there's isn't much special about them.
    • Likewise, species in Warhammer 40,000 are incapable of interbreeding naturally (though in the very first edition there were hints at human-eldar hybrids, which have been zealously purged in the quest to keep the most humanoid of 40k's alien races as alien and inhuman as possible). Some Tyranid organisms do incorporate DNA from other races to achieve certain effects however, like the spore-firing Biovore (Orks) and highly psychic Zoanthropes (Eldar).
  • In Machinations of the Space Princess, you get three species-like traits for free (water-borne, cyborg, gaseous mass, and so on). Picking a fourth drops your CHA by an appreciable amount, and a fifth even moreso, because CHA is more a gauge of your relatability than anything else and the more hodge-podge your character is, the harder it is for other species to click with them.
  • In Hc Svnt Dracones, Vectors have "mutt-reduction protocols" written into their genomes that normally allow different species to interbreed without hybridizing, instead producing offspring of one species or the other. But on rare occasions hybrids are produced, and are almost always sterile.
  • In Shadowrun, the four Metatypes (Elves, Dwarves, Orks and Trolls) can freely interbreed with each other and with baseline humans. However, such unions always result in children who possess one of their parents' metatypes (for example, an elf can be the sibling of a dwarf).

    Video Games 
  • Through Developer's Foresight in Creatures 2, it is possible for the cute and fuzzy norns to interbreed with the pesky ettins and grendels if a mod is applied to change breeding behaviors, but the offspring (which will have different body parts from each parent) will almost always die at birth. Averted in Creatures 3, however; there's even a Splicing Machine to force crossbreeding.
  • The Elder Scrolls
    • In the lore, two different races reproducing will result in a child with the race of the mother, with a few of the father's traits sprinkled in, such as a slightly taller Imperial due to an Altmer father. On its own the trope is played straight, but interbreeding over thousands of years between the Direnni Aldmer (biologically Altmer) and Nedic humans (essentially proto-Imperials) resulted in the magically talented but otherwise human Bretons.
    • Throughout the series, Vampirism and Lycanthropy are both diseases which can be spread like any other. However, each makes you immune to all other diseases, making them mutually exclusive.
    • In Skyrim's Dawnguard DLC, becoming a Volkihar Pure-blooded vampire will forcibly cure you from Lycanthropy. Becoming a Pure-Blooded Vampire however means consuming the blood of another Pure-Blooded Vampire, forcibly "overwriting" Lycanthropy's 100% disease immunity feature. This vampirism can later be overwritten by another dose of werewolf blood offered by Aela. Alternatively, you can take advantage of a nifty exploit that involves having Serana turn you, becoming a werewolf, and immediately becoming re-infected to become a true monster hybrid.
  • With the exception of ghosts, the various supernatural/occult/sci-fi life states in The Sims 3 (vampires, werewolves, aliens, etc.) are deliberately coded to be mutually exclusive. (Or at least, they should be.) This was done because it was entirely possible to combine all the life states into one sim in The Sims 2 and it was kind of ridiculous.
  • Humans in Arcanum: Of Steamworks & Magick Obscura are capable of interbreeding with orcs, elves and ogres, resulting in half-orcs, half-elves and half-ogres, because those races are descended from humans who were mutated by exposure to large amounts of magic in the ancient past and share enough human DNA to create viable offspring. The other races in Arcanum (dwarves, gnomes and halflings) have their own family tree and cannot interbreed with humans.
  • In StarCraft, this is the justification in-game for the Zerg's ability to infest Terrans not working on Protoss: since Zerg and Protoss pretty much are polar opposites down to the genetic level, it's impossible for their DNA to be combined, and as such for the former to assimilate the latter. One of the major plot points involves the Greater-Scope Villain's Dragon finding a way around this and trying to create a new, powerful race of Hybrids.
  • In Fire Emblem Fates, if you marry Corrin (a half-dragon) off to a Kitsune or Wolfskin, their children will be a mix of human, dragon, and Kitsune or Wolfskin. However, said children can only transform to either beast or dragon, and will have weaknesses to both anti-dragon and anti-beast abilities.
  • In Monster Girl Quest, a monster and human will almost always have pure monsters as children, with a rare chance of having a human with a trace of monster blood. There is only one case of an angel-human pairing, which resulted in a half-human half-angel (angels are normally produced by means other than natural reproduction). Both monsters and angels are all-female, so they can't interbreed, and this is reinforced by the incompatibility between the dark energy of monsters and the holy energy of angels. One of the villains' goals is to find a way for one being to use both dark and holy power.
  • Slime Rancher will let you hybridize two Slimes by feeding one Slime the plort of another Slime. This results in a Largo Slime, which will have visible traits from both parent Slimes, can eat anything they could have, and pops out both types of plorts when fed. Trying to increase the effect by feeding a Largo a different plort will result in a Tarr — a massive, carnivorous monster that eats Slimes (and will even try to snack on you), and instead of giving plorts, will just split in two every time it feeds.
  • Merging the titular magic gems in Gemcraft to create a more powerful one is a core gameplay mechanic, and fusing together two pure gems of different colors creates a dual gem with larger stat bonuses as well as the specials of both colors. Merging more colors into it, however, negates the bonuses altogether.
    • This varies a bit from game to game, explained by the different protagonists expressing the magic of gems and colors in different ways. Later games will usually let you mix any set of colors, in any available proportions, and get a gem which technically inherits all of its ancestors' traits. The power of specials does always drop off sharply with each new color mixed into a gem, and it's very possible for the effects of a color to diminish to an extent that the gem info no longer bothers to mention them (even though the traces are still there). It's still sometimes worth doing things this way.
  • In Stellaris, the three mutually exclusive Ascension Paths grant the empire a unique species bonus: Cyborg for the Synthetic path; Psionic for the Psionic path; and a series of powerful unique traits for Genetic. Due to the way genetic modification worked, it was possible with some tweaking to get traits from two or all three paths on a single pop and then spread it to their entire race. Paradox stepped in by making it so unique traits such as Cyborg and Psionic could no longer be added or removed for a pre-existing pop, curtailing the player ability to create these hybrids.
  • In Endless Space 2, the Horatio's Gene Hunter ability allows them to sacrifice pops of other races living in their empire to enhance the main Horatio pops. This is limited by the fact that each use of the ability permanently increases the required sacrifical pops by two. While two pops is easy to provide, after just a few uses it will take the populations of entire planets and later systems to gain new boosts. Eventually it simply becomes impractical to try and supply enough pops of even the most useful race instead of just replacing them with Horatios.

    Web Comics 
  • The vampires in Last Blood are immune to zombie bites, making them unlikely defenders of the remnants of humanity. Of course, that has to do with zombies being created from a starved vampire's bite.
  • Rusty and Co. warns about the consequences of allowing players to multiclass freely in a system that has "monster classes", as the picture above shows. He gets worse. Much worse.
  • Slightly Damned: All five races of Medius can breed with each other no matter how different they are, although their offspring will usually be infertile. It has been confirmed by Word of God that demons cannot breed with Medians, and the same is probably true for angels and Medians. It currently is not clear if demons and angels can interbreed, though one pair has tried without success, although this might be due to both races having fertility issues. More likely, this is probably due to the way that souls work in the setting. Medians have souls made by all three of the gods, while angels and demons each get their souls from only one of the gods, Gaia for angels and Syndel for demons. So a hybrid where one or both parents were an angel or a demon probably couldn't exist unless the gods made a new kind of soul.
  • Zoophobia's Zill is a demon/dragon/chimera-mutt, though the only obvious physical characteristics of these are his retractable wings and snake tail.
  • In Skin Deep pretty much any two species can interbreed (using the human-form medallions if necessary), but under normal circumstances the kids will simply be one species or the other.

    Western Animation 
  • In My Little Pony: Friendship is Magic, the various species of ponies can (apparently) interbreed; however, it seems that crossing pegasi and unicorns results in either pegasi or unicorns, not both, and (allegedly) there are earth ponies who have pegasus and unicorn ancestry, which can come out if two with sufficient ancestry get together. In the one example from the show of this actually happening the only pegasus ancestor the father knew of was related by marriage, not direct descent. It is unclear whether this dilution of bloodline impacts the potency of the children, or whether they get any of the enhanced strength and endurance of earth ponies. Alicorns - ponies with both unicorn horns and pegasus wings, and indeed, typically speaking -larger- versions of each - do not seem to be natural creatures, instead being a sort of Physical God and far more powerful than either pegasi or unicorns. It seems that the status comes with sufficient power, though the exact criteria are unclear. Twilight Sparkle becomes one at the end of the third season, growing a pair of wings. Season five introduces Flurry Heart, daughter of Princess Cadence and the first natural-born alicorn in Equestrian history.

    Real Life 
  • Many real-life hybrids (mules, hinnies, zorses etc.) are themselves sterile. With big cat hybrids, this is actually Zigzagged: while male hybrids are sterile, some females can be fertile and produce Uneven Hybrid offspring with either of their parent species, resulting in li-ligers, ti-ligers, li-tigons and ti-tigons. Hybrids of the common bottlenose dolphin and false killer whale are also fertile, as are dog, wolf and coyote hybrids.