Demogorgon

The Demogorgon is a grotesque creature from a parallel dimension known as the Upside Down.

Biology
The Demogorgon is mostly humanoid in stature and body shape but with thin, fleshy skin with bones visible. Some body parts, such as the arms, legs, fingers, etc. is more elongated, making it appear taller than a normal human. One of the more noticeable aspects of the Demogorgon is its massive gaping mouth with circular rows of teeth and several jaws that, when together, resemble the shape of a butterfly or flower.

Abilities
The Demogorgon has the ability to travel to and from Earth and the Upside Down by using rifts that it is able to create. Much like the other creatures of the Upside Down, the Demogorgon has a sort of hive mind connection with the denizens of the Upside Down, such as the Mind Flayer, Demobats, and the fungal and flesh-like environment that it inhabits.

Slug
While in stage one, the demodogs look very black larvae, appearing to be dirty, after a while parasitizing a living being it reaches stage two, which seems to take a while since there was a gap of some years between Will's spit in the sink and find it in the trash.

Pollywog
It logically gets bigger and creates a tail, takes on a more greenish color and two forelegs, has no eyes, nose or ears, but has a very small mouth to feed on.

Frogogorgon
At this stage he grows a little more and two hind legs "jump" out of his body, he takes on a more greenish color and is about the size of a frog.

Catogorgon
In stage four it starts to get more interesting, he sheds his skin (similar to what snakes do) looking like a demogorgon, having his legs more developed, he grows in size getting a little bigger than a cat, he develops a neck, and its head remains without eyes, ears or nose, however, its mouth grows much more and now it has the capacity to open in several parts, being in the shape of a star when opened, with several rows of teeth in each corner of the mouth.

Demodog
It grows much more, getting to be compared to larger animals like wolves, but otherwise its appearance remains the same, only decreasing the size of the tail.

Demogorgon
Upon the sixth and final stage it has now grown to plantigrade humanoid bipeds and completely looses its tail. An adult Demogorgon are substantially stronger and is enable to travel through dimensions randomly.

Hunting Methods
Since the Demogorgon is non-sapient, it mainly acts as more of an animal than a sentient creature. The way the Demogorgon hunts down its victims on Earth is reminiscent of how a shark hunts its prey. Like a shark, the Demogorgon can detect blood on Earth despite currently being in the Upside Down, once he detects the blood, it then travels to Earth and take its victim to the Upside Down where the Demogorgon will either eat its prey or impregnate it with it's larvae by keeping its victim in a sedated like state.