Stephen King's IT introduced readers to a one-of-a-kind creature that can take any form, the most common one being Pennywise the Dancing Clown, and as menacing as it is, this creature has one big enemy it's truly scared of: Maturin, the turtle.
Its natural enemy is the "Space Turtle" or "Maturin", another ancient dweller of King's "Macroverse" who, eons ago, created the known universe and possibly others by vomiting them out as the result of a stomachache. The Turtle appears again in King's The Dark Tower series.
Coulrophobia is no laughing matter. This irrational fear of clowns can cause panic and nausea. Although it's a rare phobia, many people find clowns creepy if not downright scary. Why? The answer lies partly in the prevalence of evil clowns in popular culture—think Pennywise in Stephen King's It (1986).
That is, when Pennywise morphs into a werewolf, he is subject to the same weaknesses as a werewolf, including silver slugs. In both the original novel and made-for-television adaptation, Pennywise is weakened using silver bullets melted down from earrings.
In the novel, it's explained that Pennywise targets children because their fears are less complex than those of adults, allowing It to easily take the shape of whatever its victim fears.
IT arrived on Earth through an event similar to an asteroid impact, landing in what would later become Derry, Maine. Once there, IT adopted its usual pattern of hibernation that lasted between 27 and 30 years, awakening to kill and eat and then going back to sleep.
They reach the conclusion that Pennywise has all of the adults under some sort of spell that prohibits them from seeing him. The adults of Derry are shown to be villainous in their own right as well. The adults of Derry are shown to be true villains of the story in the same way as Pennywise.
The rest of the group realizes they can defeat it by shrinking it and therefore weakening it, which they achieve by standing up to it. They take out IT's heart and proceed to crush it, finally killing it. Eddie dies and his body is left behind.
It feasts on the flesh of humans simply because our fears are easy to manifest and they make us taste better. According to It, when humans got scared, "all the chemicals of fear flooded the body and salted the meat".
The turtle is a force of benevolence and is guided by compassion, whereas IT represents chaos, evil, and fear. They are diametrically opposed. Because they are both interdimensional entities with equal powers, the turtle could kill IT if it wanted to, therefore it's understandable that IT is terrified of it.
If you want to get technical, It is an alien, but It's origin goes well beyond that. It is actually an ancient cosmic deity. A god of destruction, not just of our world, but of multiple worlds and even multiple universes.
Georgie's death was unique in It. While Pennywise's later victims were composed exclusively of high school students, Georgie was only six when he died. The added horror of killing someone so young and innocent immediately established Pennywise as a terrifying villain.
Though there are some IT characters just as scary as Pennywise, the film's main villain proves to be its deadliest, with a kill count that actually reaches into the tens of thousands. Reddit user u/angelholme estimates that Pennywise actually took the lives of between 12,117 and 18,011 people.
Pennywise does not need to scare his victims in order to kill them, he simply prefers to. The reason he does this is because it supppsedly tastes better. He says it's like "salting the meat." Pennywise feeds off the fear as much as he does the consumption of Children.
Now, when the Losers crushed IT's heart while in its spider form, they killed IT's physical form and severed its connection to Derry, thus why the town was destroyed, but the true entity still lives in another plane of existence.
Kersh is Pennywise's daughter. Or at least the daughter of the man who originally had Pennywise's face. Additionally, the trailer offers a first glimpse of Bill (James McAvoy), Ben (Jay Ryan), Richie (Bill Hader), Eddie (James Ransone), and Mike (Isaiah Mustafa) back together.
(According to King's book, Pennywise actually is a spider—sort of. That's really just the closest visual approximation to what Pennywise's true form actually is, at least to our puny human minds.)
As many as billions of years old, Pennywise originated in a realm outside the known universe called the “Macroverse.” Though not confirmed, it's been suggested in the “Dark Tower” series that Pennywise was created by a being known as “the Other,” which may be the godlike figure known as Gan, who is also the embodiment ...
He's a demon and the general idea is if you are not scare, it will only be harder for Pennywise to kill you as he needs to bait you. He can kill you if he wants to anytime and doesn't care. Although, if you are not scared, he will either leave you be for a little while or just kill you in the instant .
The novel explains that IT landed on Earth during an asteroid impact and established itself under the land Derry would be later built on, and initially preyed on indigenous tribes. From that point of view, IT/Pennywise would be billions of years old, but his clown shape wouldn't be that old.
So in this case, Pennywise is an entity that feeds on fear and fear actually gives him power, but he needs a constant supply of it, otherwise his physical form weakens and can eventually be destroyed.
