"Nor exactly a bird?"
"What shall I be?"
"You will be a Betwixt-and-Between," Solomon said, and certainly he was a wise old fellow, for that is exactly how it turned out.
Some creatures are not exactly a thing, because they partake of the natures of two different things. The term for this is "liminality", from the Latin limen or threshold, and beings who remain perpetually on this threshold are mysterious, uncanny, eerie beings — if the artist uses them for their full potential. They can also appear just for the Rule of Cool (but beware the dangers of Ninja Pirate Zombie Robot). This makes this a Super Trope of many, many, many tropes.
Shapeshifting or other changes into and out of determinate states is still liminal if the transition keeps happening, or if the time in the other state confers a permanent change in the character.
They are also notorious for Loophole Abuse and No Man of Woman Born, particularly for the Impossible Task. If a task can be performed by neither one thing nor the other, it can often be done by someone who is half one and half the other.
Most liminal beings take the chaos side of Order Versus Chaos. Lawful ones tend to be the guardians of the boundaries they cross and often are immensely powerful.
Compare and contrast Werebeasts, which can change from being fully one form to fully another; in other words, they're either/or while Liminal Beings are both/and.
Tropes of liminal beings
- Child of Two Worlds: A member of two very different, often opposed, communities who may have trouble fitting completely in with either one.
- Cyborg: Mechanism and organism welded into one entity.
- Disability Superpower: Both having the advantage and being at a disadvantage.
- Blind Seer: They see with only the inner eye.
- Double Consciousness: A Liminal Being torn between the two states.
- Feathered Serpent: A feathered serpent basically unites the heavenly and the terrestrial in one being.
- Flying Dutchman: Trapped in endless travel through space, time, and the realms beyond.
- Gender Bender: Goes from one biological sex to another.
- Hermaphrodite: Someone with both male and female sex characteristics.
- Heroic Bastard: Neither of his parents' social status, nor exactly not of it.
- Master of Disguise: A character of many faces and identities.
- Mix-and-Match Critters: Part one critter, part not. Also sometimes known as a "chimera."
- Hybrid Monster : Many species, one monster.
- Mixed Ancestry: Someone who is descended from two or more different ethnicities/species.
- Non-Linear Character: Both in and out of time
- Not Quite Human: Just like a normal human, except for one obvious difference.
- Otherworldly and Sexually Ambiguous: A god, demon, or otherwise otherworldly being or creature who is both male and female. Or neither.
- Oxymoronic Being: a living self-contradiction
- Paradox Person: They exist, when they shouldn't.
- Planimal: Both plant and animal.
- Psychopomp: Often the only being capable of crossing between the worlds of the living and the dead.
- Secret Identity: Ordinary person, living among ordinary people, and superpowered wonder.
- Semi-Divine: Has an "essence" that is partly mundane and partly supernatural.
- Shapeshifting: A being that is capable of modifying its own physical form, often radically.
- Trans Nature: They're uncomfortable with whatever role they've been born into or assigned to and wish to change it.
- The Trickster: Frequently, particularly in older myths, have a theme of guarding/crossing/exemplifying the thresholds between gods/humanity, good/evil, life/death, male/female etc.
- The Undead: Both dead and alive.
- Uplifted Animal: an animal gifted with human intelligence. Opinions vary on whether this is a good gift or not.
- When Trees Attack: Sessile plants with motion.
- Wild Card: On the moral border.
- Wise Tree: Both a plant, and with a mind.
- You Cannot Grasp the True Form: Both comprehensible/experienced — and not.
Liminal beings that fall between the tropes
- Schrodinger in Hellsing, a catboy who, due to being a result of a Nazi experiment, has a loose grasp of causality; he both exists and does not exist.
- In the French tale "The Valley of Damned", the character the couple meet on the borders of the valley is dressed half for town and half for country.
- Tiresias, when Odysseus consults him in the underworld, manages to hit a trifecta of liminality:
- A ghost, both alive and dead
- A blind seer, both less and more than human in his abilities, and
- Having been transformed into woman and back while alive, both male and female.
- Tobias from Animorphs, with his human and hawk dual natures, plus his Andalite heritage.
- The "scramble suits" worn by drug enforcement agents in A Scanner Darkly were thin membranes projecting constantly-shifting images of different physical and facial features over the bodies of the wearers, to provide anonymity.
- In Katherine Addison's The Goblin Emperor, a woman had been formally betrothed to a prince when he died, but not actually married him; this detached her from her own family without incorporating her into his. Maia contemplates her status as this, and there are suggestions that she could become a votary (dedicate herself to a god) as the simplest way to handle her situation.
- In Madeleine L'Engle's A Wrinkle in Time, when Calvin and Charles Wallace first meet, Charles Wallace explains to Mrs Who that Meg has it tough because she's not really one thing or another — neither, like him, comfortable dealing with Mrs Who and others like her, nor not involved at all
- In A Discovery of Witches, it turns out that Diana Bishop is a being of opposites in several ways — thanks to Vanishing Twin Syndrome, she's a genetic chimera with DNA of her unborn twin brother. She then saves Matthew's life by giving him some of her blood, and patches of her body turn cold, like a vampire's. In the second book, it turns out she is a weaver (capable of using all paths of witchcraft, but never mastering them), with an affinity for fire and water, and capable of standing between the realms of life and death, and past and future. In the third book, it's revealed that weavers themselves are the result of daemon and witch DNA mingling — and Diana merges with the Book of Life, to become a book and a woman, the history of the four races and the hope for their future. Phew!
- In Ursula K. Le Guin's The Farthest Shore, they find that someone is offering that one can escape both life and death. In the end, he claims to be between both and so free of them.
- Terry Pratchett's novels:
- In Witches Abroad, Mrs. Gogol starts her invocations with the observation that she is between light and darkness, which does not matter because "I am between."
- In The Wee Free Men, the "hag of the hills" is supposed to look after edges and gateways. At the end, the witches tell Tiffany that witches are supposed to look after edges.
- Rick Riordan's novels:
- In The Sea of Monsters, Chiron points out that Divine Parentage for humans (as opposed to cyclopes and other such creatures) puts them on two levels at once, human and immortal.
- In The House of Hades, Hecate — while standing at a crossroads — tells Hazel that having died and come back to life gives her still more control over the veil between the two worlds.
- In Lord Dunsany's The King of Elfland's Daughter, having been across the border to the mortal lands and back means Lirazel can not be content in either land
- In John C. Wright's Green Knight's Squire, the Moths and Cobwebs are part human, part fae. They are known as the Twilight People as a consequence, and fall between worlds in many ways.
- The Graveyard Book:
- The protagonist, Nobody Owens, is a human child raised by ghosts, which gives him access to the worlds of the living and of the dead. When he reaches adulthood, he has to choose once and for all which world he will belong to.
- Silas (who is strongly implied but never quite stated to be a vampire) also exists between the living world and the dead, but unlike Bod, who belongs to both worlds, Silas belongs to neither, which occasionally has drawbacks.
- In Harry Potter and the Order of the Phoenix Nearly Headless Nick reveals that this is what it means for a witch or wizard to become a ghost, to be stuck between life and death and have chosen not to move on for a flimsy approximation of life.
- In one of Aesop's Fables, a bat tries to ally with both beasts and birds, trading on its similarity to both and disavowing the other traits according to whom it's addressing, but after the war, they unify in rejecting it from both groups.
- In Indian myth, Vishnu became a half-man, half-lion in order to deal with a demon that could not been killed by an animal, a man, or a god, neither by night nor by day. (He also did it at sundown.)
- According to Christian doctrine, Jesus Christ is "fully God and fully Man". The official doctrinal term is the hypostatic union, meaning Jesus was one individual person who had two natures, a divine nature and a human nature, 100% of each. The ideas that he was God but appeared to be human, or that he was a human who became God, are rejected by most branches of the Church as heretical, though not without a fair bit of controversy.
- In the Western Zodiac, a few signs hinge between forms, either obviously or implicitly. Capricorn is depicted as a goat with a fish's tail, therefore being between earth and sea. Sagittarius, depicted as a centaur, is half-human, half-animal, furthermore always aiming towards heaven with their bow, therefore a being between three worlds. Gemini is a pair of twins, Castor and Pollux, of whom one is mortal and the other is divine, but they'll do anything to stay together. Aquarius, "The Water Bearer," is actually an Air Sign; in mythology Aquarius is Ganymede, a human prince who was kidnapped and made to be a servant of the gods.
- In the Tarot deck, more than a few cards dwell between worlds, or between states.
- The Fool is a clear example, standing outside the numbered cards, at both and neither the beginning and the end, note with symbols of creation and destruction.
- The Hanged Man is a card full of paradoxes: he is between life and death, sacrificed, but still alive; he dangles between worlds, yet sees all of them clearly; bound, his mind is freed.
- In Diablo III's "Reaper of Souls" expansion, Malthael, Angel of Death, is said to be in a state of superimposed life and death, allowing him to attack people or even suck out their souls while their weapons pass through him harmlessly. In the final part of the act, the player-character must counter this by receiving help from a group of powerful ghosts, giving them the same attribute.
- Many characters in Ghost Trick invoke this trope, but possibly no one embodies it as much as Yomiel. Stuck between life and death due to the Temsik meteor fragment lodged in his body, Yomiel can neither live nor die, and the isolation eventually drives him insane.
- Touhou has Yukari Yakumo, the youkai of boundaries, who has perhaps the single most broken Semantic Superpower in a series filled with them. She can manipulate boundaries (Gensokyo/the real world, truth/illusion, Earth/the Moon, life/death...), manifesting mostly as Thinking Up Portals (holes in reality where and whenever she wants. Call her the gap hag at your own risk). Thankfully she spends most of her time sleeping and playing stupid pranks on people.
- In Gunnerkrigg Court, when Annie and Kat ask Jones whether Zimmy is human, Jones says not that she is, or isn't, but that she is for all practical purposes. Zimmy is in many respects more uncanny and creepy than most of the overtly non-human beings in and around the court.
- In Bird Boy, the woods, which are actually called the liminal woods.