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. Transitioning out of being a liminal being is difficult if even possible. See the Liminal Time YKTTW for when transition is normal.
Tropes of liminal beings
- Disability Superpower: Both more than human and less than human in ability
- Flying Dutchman: Trapped in endless travel
- Gender Bender
- Half-Human Hybrid: both human and not
- Heroic Bastard: Neither of his parents' social status, nor exactly not of it.
- Mix-and-Match Critters: Part one critter, part not.
- Non-Linear Character: Both in and out of time
- Planimal: Both plant and animal
- The Undead: both dead and alive
- You Cannot Grasp the True Form: Both comprehensible/experienced — and not.
Liminal beings that fall between the tropesAnime & Manga
- 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.
- 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.
- Torchwood had Owen, who died and Came Back Wrong. He wasn't really alive or dead, so he couldn't be killed, couldn't heal from injuries, eat, etc etc
- 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 who it's speaking to, but after the war, they unify in rejecting it from both groups.
- Ciel from Tsukihime is stuck between life and death, due to not having died after the Big Bad possessed and left her body, like all his previous victims did.
- Balto has it verbalized by Boris about the title character. "Not a dog, not a wolf...all he knows is what he is not."
Hello, Unknown Troper. You'll need to get known to lend a hand here.