Hybrid Overkill Avoidance

Don't do this. Ever.

"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

Everyone likes 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; while cyborg-demons are awesome, a were-wolf / fish man? Not so much.

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 fire elemental / half vampire.

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 half 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 further mutation. Robots won't become ghosts because, y'know, no Soul.^[1] 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. And sometimes the offspring only inherits one of their parents types, or a few, but not all, of either's traits.

Examples of Hybrid Overkill Avoidance include:

Anime and Manga

• 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 turns into anything she bites with them.
• Normally Yu-Gi-Oh! allows just about any two summoned monsters to be fused together; however there is one interesting case where it's played disturbingly literally in the first tournament. Yugi defeats Kaiba's Blue Eyes Ultimate Dragon by fusing his Mammoth Graveyard (an undead type) into it... which, because both are incompatible types, was slowly weakening the resulting fusion and would cause its eventual death. After this, the rule is never referenced again.

Comic Books

• In Marvel Zombies, Werewolf By Night is saved from zombiism because, despite being vulnerable in human form, he's immune in werewolf form. So magically creating moonlight to trigger his transformation cured him.
  • Directly subverted earlier in Marvel Zombies' Ninja Pirate Zombie Robot moment, in which Alternate!Morbius exclaims, "I am a VAMPIRE! I am a ZOMBIE! I am a VAMBIE!"
    • Morbius isn't an actual undead vampire - he's a living person (or in that case, zombie) with vampire-like traits and powers. Hence his nickname "Morbius, the Living Vampire."
      • Though, since this is an alternate Morbius, he may be a true vampire instead. He does die from a stake to the heart after all. Then again, that works on the living too.
      • Good thing he got that Lilan (demon) blood out of him years ago!
• The aversion of this is a major plot point in IDW's Crisis Crossover Infestation. A Genre Savvy US government decides the best way to deal with a scientist accidentally opening a portal to a zombie dimension is to send in their vampire agents backed by robots. Unfortunately, this particular zombie outbreak *did* affect vampires and robots. Oops. Cue one zombie plague spreading to the worlds of Star Trek, G.I. Joe, Ghostbusters, and Transformers. That's right, there were zombie Transformers.
  • Britt's Transformer form is effectively a Ninja Vampire Zombie Robot (insofar as CVO agents count as ninjas).
• Averted in one instance in Buffy the Vampire Slayer Season Eight: the minor villain Kumiko is a vampire witch.
• In Young All Stars, there's an Axis agent called Sea Wolf, a water-breathing werewolf.

Film

• The Underworld movies have this trope justified through biological incompatibility. Once they find a guy who has the genetic traits allowing for both werewolf and vampire genes, however...

Folklore

• In some parts of Europe, it was thought at one time that the corpses of werewolves would rise as vampires if they weren't cremated. In other parts, the corpses of dead sinners were said to become blood-drinking wolves at night. In Serbia, werewolves and vampires are collectively referred to as the same creature.

Live Action Television

• 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.
• Vampires in Being Human (UK) 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.
• In Buffy the Vampire Slayer, the eponymous Slayer is considered a human monster (having been infected with demonic blood by the Shadowmen, 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 Slayer 'verse, as most vampires would prefer to kill a Slayer than turn her.

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. They already have powers, so the desperation to take up the vigil never comes to them. Only humans can be embraced, not spirits made flesh (which is one explanation as to why some embraces don't work: that might have been a werewolf who hadn't undergone their first change). Having what may very well be a minor god of death living in your soul is one of the best ways to keep yourself from being consigned to unlife, providing you're lucky enough to get one's attention and you're willing to make the deal (In addition, Sin Eaters can innately see the dead and how old someone is [vampires register as dead to these senses], if you're a Vampire and walk past a Krewe of Sin Eaters, they'll know something is up almost automatically and more often then not try to destroy you for being an Undead creature who feeds on humanity. ). Lastly, not having the spark of true human life anymore, they can't awaken to true magic.
    • 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 Blood, effects may wary) or other effects.
    • Werewolves are spirits of the hunt / of rage / of protection / of death who were forced to take on human forms by way of a curse laid down on their ancestors / god(s). 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 the Prometheans. 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 too (to say nothing of their psychologies, which may be less resilient). And again, no human desperation equals no vigil.
    • Vampires, werewolves, Prometheans, changelings 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 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. Also, they lose nearly all Promethean abilities upon attaining humanity.
      • 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. Its 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.
  • The Old World of Darkness has similar rules to the above to prevent gratuitous crossover:
    • 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, even if they resemble humans or animals at birth, so they lack avatars. When they die they can't go to the same afterlife as human dead, so they can't become wraiths, zombies, or Kindred of the East.
    • One exception is a vampire-werewolf hybrid "abomination," extremely tricky but possible. Werevolves 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 but has to watch the Karma Meter very carefully - from 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. This can be used offensively (and werewolves destroy vampires in combat bad enough this isn't your worst option), but may only be Taking You with Me.
    • Several other Changing-Breeds either can't be embraced, or can't stay that way for long afterwards. Kitsune were-foxes explode in fire if embraced as kind of a Take That to players' obsession with making abominations. Corax were-ravens? They explode come dawn no matter WHERE they are. Mokolé were-dinosaurs? They go BALLISTIC the second the embrace starts, and their war form? A dragon/dinosaur which may very well breathe fire and/or glow with sunlight. Then they die. Rokea were-sharks? No vampire has been dumb enough to try it (they also are mostly aquatic, making it hard for vampires to even know they EXIST, much less find and capture one). Bastet werecats can be embraced but immediately start losing their Gnosis stat, which cripples their supernatural abilities.
    • The one accepted hybrid is anyone except an imbued hunter can drink a vampire's blood and become their ghoul, which is generally a bad thing since it makes them the vampire's bitch (or for the handful of independent ghouls that bleed and kill vampires to drink their blood bond free, renders them essentially a junkie serial killer). For a Mage the blood addiction slowly kills their avatar and ability to do magic along with it. There's mention the Rafastio family of Revenants ^[2] has some members that are also mages.
    • Also averted by the infamous Canon Villain Sue Samuel Haight who was a ghoul-werewolf-true mage. Until he died, became a ghost, and was soulforged into an ashtray.
• Some templates in the 3rd Edition D&D 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. You can make an undead from a lycanthrope, but it tends to be pretty pointless since they revert to their human form upon death and none of the bonuses they get from being an untransformed lycanthrope are maintained by the transformation into typical undead. The result is just a human.
  • 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.
  • 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.
    • Only one crossbreed half-dragons is known to have occurred in Eberron, and she considered an abomination worth destroying her entire bloodline over. Half-dragon as a template is applied exclusively to fiends "blessed" by Tiamat.
  • It is possible to graft construct parts onto a living creature, but the result becomes a construct 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.
    • 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) 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. Also the trollbane item makes what it's applied to bypasses regeneration regardless of damage type.
  • 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. Thus a 1st level half-dragon character is theoretically as powerful as a 4th level character, and as such 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. Only a max of +1 or +2 level adjustment is ever practical (since this can be removed entirely at high levels) and the sources of level adjustment are worth the level adjustment can be counted on your fingers.
• 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.

Video Games

• Averted in Paladin's Quest (and the sequel, Lennus II.) There are Loads and Loads of Races, and they can all interbreed. Hybrids are called Lubbots, and are considered a race of their own because interbreeding is taboo in most societies. There's an entire village of hybrids in one part of the world.
• Becoming a werewolf in Skyrim will cure you of vampirism, and give you an immunity to disease that will stop you catching it again.
• In Dwarf Fortress interactions that turn a creature into werebeast, vampire or "disturbed dead" all are made explicitly unappliable to the targets already afflicted by any of them, as well as a few broader classes.

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 consequences of allowing to multiclass freely in the system that got "monster classes", as the picture above shows. Later he got worse.
  • Everything is weirder with... Templates!

1. ↑ (Virtual Ghosts are doable, though)
2. ↑ ghouls bred with other ghouls (and possibly magically mutated) so much the offspring are born ghouls with their own vitae production.