I just came across a new one to me
https://www.vice.com/en_au/article/mvx7v8/the-berensteain-bears-conspiracy-theory-that-has-convinced-the-internet-there-are-parallel-universesThe Berenst(E)ain Bears Conspiracy Theory That Has Convinced the Internet There Are Parallel Universes
You remember the Berenstein Bears, right? Now, what if we told you they never existed?
Yeah, because it was spelt
Berenstain, which is a less familiar spelling, so lots of people confuse the spelling. I thought it was Berenstein, and we had one of the books as a kid, though it wasn't a big part of my childhood. The explanation of why this is so common is most probably because of a combination of the repetition of the e's in the name, coupled with the limited reading comprehension of children who were exposed to the books (it's a long name for a small child), along with the common "stein" ending for names. It's not helped, because apparently the name itself is misspelled on some of the old VHS tape labels - one example has "b-stain" on the front and "b-stein" on the top, which shows a common cultural confusion over the spelling.
However, rather than contemplate the theory that their memory is a tiny bit off, or they just never paid that much attention in the first place, people have posited that they've actually been teleported into an alternate dimension in which the only change is the spelling of a 1960s children's book franchise.
Although the words were written in jest, the writer—the false prophet—blows the whole Berenstain Bears theory open and relates it to the Butterfly Effect.
"At some point between the years 1986 and 2011, someone traveled back in time and inadvertently altered the timeline of human history so that the Berenstein Bears somehow became the Berenstain Bears," he wrote. "This is why everyone remembers the name incorrectly; it was Berenstein when we were kids, but at some point when we weren't paying attention, someone went back in time and rippled our life experience ever so slightly."
Little did he know how important that notion would come to be in the movement.
The next appearance of the theory came in the form of a 2012 post on the blog The Wood Between Worlds by a user named Reese, called "The Berenstain Bears: We Are Living in Our Own Parallel Universe." These 1,600 words would prove to be the main literature of this modern movement. It is simply the Berensteinites' New Testament, their Vedas.
In it, the blog's author makes a "modest proposal," one that implies that all of us are "living in our own parallel universe." He propagates that there are at least two universes; the "stEien" universe and the "stAin" universe. The author attempts to prove the theory as true, and breaks down into mathematical and scientific terms.
The broader theory comes under the general heading "The Mandela Effect" which is a real psychological effect (a thing that many people misremember in the same way), but the conspiracy theory is that this represents slippage between parallel dimensions, or memories leaking between dimensions, or something more sinister such as a cabal of time-travellers going back in time to manipulate history, and leaving clues behind like changing quotes in popular movies.