Nix

A Nix[1] is a fictional creature from the television show American Dragon: Jake Long. It is a magical creature that is harmless during the day, but becomes a soul-sucking monster when the moon reaches the center of the night sky. The American Dragon first encountered one causing trouble in the sewers. He later found out the creature was a girl named Jasmine.

History
Jake Long took a girl named Jasmine, whom he just met, to the dance. However, he did not know she was a Nix, a soul-sucking creature. He managed to last longer than anyone else at the dance, without having his soul drained, but he drank the potion meant for the Nix by mistake, rendering him powerless. He used his breath to knock the creature out, defeating her. She turned back to her human form and later apologized to Jake profusely.

Physical Appearance
A Nix has two forms. The first is that of a perfectly normal human.

The second is a monstrous shape that only reveals itself once the moon reaches the center of the sky. In this form, the Nix' skin will turn entirely green. Its nails will turn into sharp, dark claws and its legs will fuse together to form a serpent's tail. A set of dark feathered wings will also come out of its back. Its ears will become pointy, fangs will grow out of its mouth, and its eyes will turn red. Its hair will also become wild and messy.

Magical Powers
Thanks to its wings, a Nix can easily fly around. Also, because of its slender serpent body, it is quite fast and agile. It is very strong physically, and can use its wings as a shield, mainly to protect itself from projectiles. Its tail can also be used as a whip. Nixes are vulnerable to fire.

The main power of the Nix is its soul-sucking ability. When stealing someone's spirit, its eyes will glow red, instantly mesmerizing its target. Then, the soul (in the form of a blue fog) will creep out of the victim's mouth and pour into the Nix. Those whose souls have been taken will then wonder around aimlessly, unable to show any sign of awareness or intelligence as though caught in a trance.

One way to defeat a Nix would be to pour on it a potion that makes anyone who touches it completely powerless. Another way that proves effective (as demonstrated by Jake) is to expose the Nix to a Dragon's breath, which will make the beast suffocate from the rancid smell. Once the Nix is knocked out, it will lose all the souls it stole and will transform back to its human self. The stolen spirits will then automatically return to their true bodies (except for Spud and Trixie who get their souls mixed up with each other, although this gets fixed off-screen). A Nix will also return to its human form once the moon sets.

Life in the Magical World
Since a Nix is often times incapable of controlling its monstrous side, it is not considered inherently evil. This is proven by the fact that Jasmine sincerely apologies to Jake about the incident involving her Nix form during the Fall Dance he had invited her to. It is to avoid these kinds of situations that Nixes often stay indoors during the night.