Well, the Mandela Effect origin story is centered around the strange phenomenon related to Nelson Mandela. People wrongly remembered his death as being much earlier. Some say it might be because of glitches in the matrix - which is more of a science - fictiony idea. But more likely, it's about how we as a society consume and mis - consume information. Media can play a big role. If there was some misinformation spread at some point, and it got repeated often enough, it could lead to a whole bunch of people having the same wrong memory.
Yes, there are some scientific explanations. One is that human memory is fallible. Our brains often reconstruct memories based on bits of information we've gathered over time. So, false memories can be created easily. For the Mandela Effect, if there was misinformation in the media about Mandela's life events, like the time of his death, our brains could have incorporated that wrong info and created a false memory. Another aspect is that memory can be influenced by suggestion. If people around us believe something a certain way, it can sway our own memories.
C - 3PO was created by Anakin Skywalker. Anakin built him as a protocol droid to assist in various tasks. He was designed to be fluent in multiple languages and to be able to interact with different species. This origin story sets the foundation for C - 3PO's role in the Star Wars saga, as he often finds himself in the middle of important events, using his language skills and knowledge to help or sometimes just get in the way in a rather comical way.
One example could be a misremembered line of dialogue. Maybe some people remember a particular phrase being said in a different way than it actually is in the movie. Another could be a scene that people think occurred in a different order. For instance, the sequence of events in the diner might be misremembered by some due to the Mandela Effect.
The 'A Christmas Story' Mandela Effect has various manifestations. For example, some recall specific lines of dialogue or character actions differently. This could be due to collective memory glitches or misinformation spread over time.
It can make people question their own memories. For example, if they remember a scene differently, they might start to wonder if they really watched the movie correctly.
Yes, in some fanfics, C3PO might recognise Darth Vader. C3PO is a protocol droid with a vast knowledge database. If the fanfic adheres to the basic Star Wars lore, C3PO would likely be aware of Vader's identity and his importance in the Galactic Empire. However, the nature of fanfics allows for a lot of creative liberties, so there could also be scenarios where C3PO's recognition of Vader is altered or not as straightforward due to some unique plot twists or alternate universe settings.
A common theme could be friendship. Rsd2 and C3PO might form an unlikely bond and help each other out. Another theme could be exploration. They could be exploring new planets or parts of the galaxy together.