Eleanor Newmann

Elliot is a dark blue creature made of slime. They have three lime-green eyes and two solid black antennae. The dark "freckles" seen on their body is actually just a collection of trapped air bubbles, which they use to feed oxygen to Eleanor.
Being made of slime, they can take on any shape they want, but typically choose to take on the appearance of an adorable, round-headed creature with "fins" extruding from the sides, somewhat resembling an axolotl. They can give themselves arms and legs, when necessary.
When inside Eleanor's lungs, they spread themselves out as thinly as possible so Eleanor doesn't suffocate. They end up coating the entirety of her lungs and stretch further up into her trachea.
Elliot has no organs, aside from a brain, their eyes, and an acid gland. Their brain serves them the way other organs would, and is the one thing keeping them alive. In order to feed their brain, they must get their nutrients from a certain source. That source being other creatures, and in this case, Eleanor herself.

Despite being an overwhelming burden most of the time, Elliot isn't evil. Leeching off of other creatures for energy is just in their nature as a parasite; they don't seem to have any malicious intentions. In fact, they, and their kind as a whole, actually make an effort to ensure the health and well-being of their host. A sick, dying, or dead host is not a good source of energy, so they do their best to make sure Eleanor is doing okay.

Elliot is the life of the party. There's not much that stands between them and having a wild time. However, Elliot is incredibly impulsive and lacks common sense. Though, with some training from Eleanor, they have a mild understanding of what is right and what is wrong.

Elliot is a prime example of a chatterbox. They love to interject and ask questions at every opportunity. Sometimes they just don't stop, resulting in some annoyances for Eleanor to put up with daily.

They're genuinely interested in Eleanor's work, and love to help her get through the day, by either actively taking part in her research, engaging in witty banter with her, or taking the wheel if she's burnt out. Elliot is easily entertained, and can even find tasks like note-taking or paperwork-filling fun, when Eleanor would otherwise find it stressful.

When controlling Eleanor, they do their best to imitate her. To not give off any signs to others that something is off. If a person they're talking to is aware of Elliot's presence, then Elliot will break character and act like themselves. They speak on Eleanor's behalf, referring to themselves with plural pronouns (We/Us/Our).

They're not the perfect buddy, but they serve as a valuable companion.

Parasitization:
Elliot is a parasite, and as such their main instinct is to parasitize hosts. The first step is to find a way into a host's body, through any available orifice (mouth and nose are preferred but any orifice will work), and settle into the host's system. Once inside, they leech from their host, stealing tidbits of energy which is used to nourish their brain, thus keeping them alive.

Paralytic Venom:
Their lone defense mechanism. Elliot can projectile-spit a venomous substance that can induce mild paralysis on contact with skin. The paralysis usually wears off on its own and a single spray isn't enough to cause life-threatening health problems.
Because Elliot chooses to live in Eleanor's lungs, they keep their venom gland close to her trachea, so if needed, they can quickly emerge and use their venom to help defend their host.

Host Control:
Elliot is capable of assuming control of a host's body.
Elliot has indeed managed to figure out how to control Eleanor's body, and is now at the point where they can connect to her brain near-instantly. They can do so whenever they like, but nowadays they ask Eleanor for consent before doing so.

When under Elliot's control, Eleanor is essentially unconscious and has no memory of whatever Elliot does. There is a way to tell when she's not herself: Her eyes darken and a loose stand of hair atop her head will resemble one of Elliot's antenna. As well, she loses her Australian accent.

Host Communication:
Elliot can form a telepathic link with their host, providing them with the only method of communicating with other species aside from their own.
When inside Eleanor's lungs, they can freely speak to her.

Universal Communication:
Elliot, like the rest of their kin, can understand almost any alien language- at the cost of nobody being able to understand their own (aside from their host). They serve as Eleanor's translator.

Salt:
Elliot is horribly weak to salt. Salt will dry them up, therefore killing them. This is their number-one fear and their main reason as to why they choose to occupy the lungs over any other organ; many creatures like consuming salt.

Burning Temperatures:
Extremely hot temperatures will cause the moisture of Elliot's body to evaporate. This will dry them up, and in turn, kill them.

Freezing Temperatures:
While not necessarily fatal, extremely cold temperatures will cause Elliot to freeze in place. They will remain in a statue-like state until they somehow unthaw.

Requires a Host:
Elliot is endoparasitic and can only nourish themself inside a host. If they spend too much time without one, they will 'starve' and wither away.