The Blair Witch is an evil entity from the same universe as Pennywise The Clown (IT)

For reference, I’m going off of the following sources:

The Blair Witch Project (Movie 1999)

Curse of the Blair Witch (TV short 1999)

Blair Witch (Movie 2016)

It (Novel 1986)

Book of Shadows is generally not considered to be canon, so I will disregard it.

General Theory

The Witch is a being from the same dimension as "It" from Stephen King's "It" (for the sake of simplicity, I'm going to refer to "It" as Pennywise) It operates under the same M.O. which is to use shapeshifting, possession, manipulation of reality, and fear as a means to feed. Children are the preferred diet, but they will prey on adults if they so desire.

Location

While Derry, Maine (the location of Pennywise) is not the same as Burkittsville, Maryland, they are relatively close in proximity. Pennywise and The Witch just happened to land in different areas off of probably the same dimensional tear, which explains why they are relatively close. Both, in their respective territories, prefer abandoned areas that just happen to have tunnel access to move around.

The Origin

Basically put, the Witch is supposed to be the spirit of Elly Kedward, who was left to die by the townsfolk under the suspicion of witchcraft in 1785. The event that caused this was the disappearance of several children. In this theory, Elly Kedward just happened to be in the wrong place at the wrong time….remember this is a time when you could do anything weird and get accused of being a witch. As the story goes, half of the town eventually disappeared and the remaining townsfolk got out of dodge. While the movie claims this as possible revenge by Elly’s spirit, I believe this is just all lumped into this particular active cycle…..

The Cycles

Cycles are very important here. Pennywise works in cycles that average between 27 and 30 years. In this active phase, Pennywise will do some killing for several years before it decides it want to go to sleep. This doesn’t seem to be a biological imperative, because Pennywise has been known to do a kill here or there in between. Believe it or not, The Blair Witch has cycles too…..they’re just different. The first known time Pennywise awoke was 1715, with its first known event being in 1740. The Blair Witch could be presumed to have first awoken in 1785, around the time of the Elly Kedward's incident. Why did The Witch start later then? Well, Blair (the old town that later became Burkittsville) was founded in 1734. Perhaps the town was so small, that the population didn’t build up enough for The Witch to care. That, or The Witch was done feasting on Native Americans and went into hibernation just as Blair was founded. The next major occurrence happens in 1825, where a small child was pulled underwater by a white hand and was never recovered. The next incident happened in 1885, when a search party looking for a missing child ended up massacred on Coffin Rock. Next came 1940, when a hermit admitted to killing several children under the direction of the Witch (more on this later). There is no doubt that there is a cycle, the only problem is determining the cycle. In Curse of the Blair Witch a historian goes on to comment that big events seem to happen every 50 years or so. While it could very well be that, it could also be said that The Witch has cycles of about every 20-30 years. the first known event from the next is a difference of 40 years. The next one is 50 years. The one after that is 55 years. The one after that (which ends up being the first movie) is 54 years. The final movie is 22 years later. So while it could just be a 50 year cycle, I would like to think that there are other deaths happening in between, but just aren’t being reported since the town is more rural, or The Witch is erasing memories.

The Locals

In both stories, there is an eerily similar vibe that you get from the interviews in Blair Witch and the investigating Mike Hamlin. People know something is wrong, but either don’t care or easily move on from horrible tragedies. If you watch Curse of the Blair Witch, particularly the parts where the film crew’s parents are frustrated with the police investigation, it sounds like it could be straight from points in IT where police just don’t seem to be putting a 100% or don’t press too far into the issue.

Pennywise, The Turtle, and The Witch????

So the Turtle is kind of important, because it establishes that Pennywise isn’t the only thing out there. Now, there are some that might say that Pennywise and The Turtle are the only beings, but there is nothing mentioned to prove they are the only ones. So why is the Turtle not battling the obvious evil that is The Blair Witch? Well, actually, The Turtle did….and lost.

Evil Biddings and the Loser’s Club that Lost

This is where it all ties together. So the 1940 incident, detailed in Curse of the Blair Witch, talks about the hermit Mr. Parr coming down from the mountains and saying “I finally did it”…When police searched his house, they found the bodies of SEVEN children. He later admitted to murdering the children under the direction of the Witch...

It just so happens to be a similar tactic that Pennywise used, except it was Henry Bowers and Tom Rogan sent to kill The Loser’s Club. The Loser’s Club had 7 members. Henry and Tom only had to kill 6 people though, because Stan Uris committed suicide when Hamlin called him.

Basically put, The Turtle picked its 7 children to defeat the Witch, but the Witch won. Perhaps the Turtle moved on to work on Pennywise since by that point The Witch was in hibernation.

BONUS

The Origin of Skin-walkers & other stuff.

Skin walkers are beings like The Witch and Pennywise. If these two just happen to be in Northeast, perhaps there are more spread out. It is reasonable to assume that without pop culture influencing early man, the thing that would most likely scare them would be beasts that could kill them. As pop culture flourished, the beings adapted.

I will close it off with the flimsiest of proof, notably the lanky monster that Lisa runs from during the end of Blair Witch. This was such a weird manifestation by the witch…..it almost doesn’t fit…..IF you’re thinking that it is just and old witch. IF you think along the lines of The Witch being like Pennywise, it makes more sense because perhaps that monster was a manifestation of Lisa’s fears….like maybe a fear of Slenderman. After all, tall slender humanoid monsters have made appearances in several horror movies lately, and it could be possible that Lisa saw those movies and that monster type struck a chord with her.

Also, it's worth noting that in IT, it is said that humans could not comprehend seeing Pennywise in true form, and would go insane or die just from the sight of IT. This is mentioned as well in Blair Witch as part of the folklore surrounding The Witch, except that one would die from fear. Close enough for a regional interpretation of the same thing, if you ask me.

Enjoy