Mister Chuckle Teeth

Mister Chuckle Teeth is the main antagonist of the revival era X-Files episode, Familiar. This episode is notable for bringing the series back to its horror roots and as such Mister Chuckle Teeth has become one of the more iconic monsters of this era, made even more so by his strange appearance and mannerisms.

History
Mister Chuckle Teeth was originally a popular mascot of a children's television series. Despite his rather creepy appearance, he was beloved by his audience, including a young boy named Andrew, who admired the character so much he obtained a doll of the character and would lovingly play with it every day. Things would change forever when he was out playing and the doll would manifest itself as a man-sized version of the doll, which appeared in a forest and lured a curious Andrew into the woods as his mother argued on the phone.

Andrew would continue to follow the demon deeper into the forest unaware that his "friend" was luring him to a brutal death, his mutilated corpse being found and sparking sufficient concern for FBI agents Mulder and Scully to be called in to try and solve the murder, the pair being famous for investigating weird or seemingly impossible cases few other agents would dare get involved in (known as the X-Files).

What would happen following the agents' arrival was a bizarre and frightening case of witchcraft as Mister Chuckle Teeth menaced the town in numerous forms (such as his human-sized "doll" form, his hellhound form and even a demonic "telletubby" creature used to lure another child to their demise).

As Mister Chuckle Teeth's reign of terror continued, it was revealed he was actually a demon who was summoned by a witch known as Anna, who wanted to get revenge on her cheating husband but lost control of the spirit, who began to sadistically target those she loved rather than her own original targets and seemed intent on destroying the town and its residents.

Soon the list of victims dramatically piles up as Mister Chuckle Teeth incites the townspeople into lynching a sex offender, tricks the Chief into killing Andrew's father (after invading his home), driving Andrew's mother (Diana) off the road via mimicking Andrew, then killing her. His final confirmed victim would be the Chief himself, who was murdered moments after learning that his wife was the witch responsible for all the horror in the town.

Anna set herself ablaze trying to undo the curse and died, seemingly ending Mister Chuckle Teeth in the process, but the episode ends with a child's merry-go-round ominously starting to spin by itself, hinting Mister Chuckle Teeth (or the spirit that allowed him to manifest) is still active.

Abilities

 * Immortality - As a spiritual entity, Chuckle Teeth is ageless and immune to all conventional harm. Only mystical means can hope to defeat him and there is likely no way to permanently kill him.
 * Ethereal existence - Mister Chuckle Teeth exists as a ghost, completely invisible and intangible - thus exists in a state out of touch with our reality unless summoned or desiring a manifest body.
 * Shapeshifting - Due to being a spirit, Chuckle Teeth can interact with the world via manifesting as any form he desires, whether it be living people, deceased victims or even characters from fiction or mythical creatures such as the hellhound.
 * Illusion-casting - Chuckle Teeth can cast realistic illusions that make people question their perceptions of reality, linked to his mind-warping capabilities.
 * Psychokinesis - Chuckle Teeth has psychokinetic abilities, since he can mutilate victims despite being a spirit. This means he must be able to take physical form, at least for limited amounts of time.
 * Mind-warping - Chuckle Teeth can drive people into temporary insanity or negatively influence their emotions, such as when he influenced the townspeople into lynching a man they suspected of killing the children.
 * Pact-forming - Chuckle Teeth can form pacts with humans, allowing him to influence the world. It is presumed he can not directly interact with reality unless summoned by a witch, hence his apparent defeat when Anna burst into flames.
 * Limited omniscience - Chuckle Teeth knows the strengths, weaknesses and personalities of almost everyone around him and can exploit them to frightening degrees.
 * Limited omnipresence - As a spirit Chuckle Teeth is not limited by space or time and can thus appear anywhere he pleases, though he seemed to be limited to the town and its surrounding woods.

Inspirations
Mister Chuckle Teeth is inspired by a number of demonic and occult legends and folk tales, most prominent being:
 * Bogeyman
 * Hellhound
 * Black Dog
 * Satan
 * Familiar

Modern legends with similarities to Mister Chuckle Teeth include several "creepypasta" antagonists such as:
 * Slender Man (a suit-wearing, abnormally tall monster who stalks and attacks children, often associated with woods and remote areas, Slender Man himself is a continuation of much older tales involving beings such as elves and fairies, who were also feared for abducting children.)
 * Possessed Media (many stories revolve around haunted, possessed or demonic media, often lost episodes of popular cartoons or shows that allegedly existed and had supernatural qualities to them, a famous example of which being Candle Cove.)