The original Yu-Gi-Oh! manga inspired a plethora of spin-offs, variants, and unanswered questions. When taken as a whole, the franchise presents a staggering amount of inexplicable Yu-Gi-Oh! mysteries, as the various card games, series, and video games often feel disparately fragmented. In the face of such confusion, the most satisfying (or at least the most fun) thing to do is consult Yu-Gi-Oh! fan theories for answers.
Are the main characters descendants or reincarnations of their Egyptian analogues? Where is Yugi in Yu-Gi-Oh! 5D's? Does the whole universe exist solely in Yugi's imagination? Is there a representation of the Abrahamic God present in the series?! With any luck, these fan theories about Yu-Gi-Oh! will help to answer all your burning questions.
Redditor /u/themightyheptagon makes a remarkable (and thought provoking) claim that Exodia, "an unstoppable mythic being of limitless power," is the God seen in Abrahamic religions:
"In the context of the game, he's 'The Forbidden One' because worship of YHWH was forbidden by the Pharaohs, but they still feared the idea of an all-powerful God who could one day free the Hebrews... His chains represent the Hebrews' [enslavement], and his name alludes to the Book of Exodus, which chronicles the Hebrews' liberation and YHWH's revenge on Egypt."
While the Most High may not live in houses made by human hands, technically speaking, none of the anime characters seen on Yu-Gi-Oh! are human.
Mr. Multilingual offers a very interesting and well thought out theory that explains how the characters of Yu-Gi-Oh! may be reincarnations of Ancient Egyptian people:
"The Ancient Egyptians believed in various components of the human being:
- The khat, the physical body
- The ka, a spiritual equivalent of the khat, which was the immortal life-force
- The ib, the heart, the seat of emotion, will, and thought
- The sheut, the shadow
- The ren, the name
- The ba, the personality
- The ba, represented as a spiritual entity with the body of a bird, and human head
Upon [his demise], the ka left the khat, and then was later reunited with the ba to form the akh. It is this unified form that enters the Afterlife. (Egyptian Mythology; 'Ancient Egyptian concept of the soul')
Therefore, my theory is that it is not the entirety of one’s person that is reincarnated in 'Yu-Gi-Oh!', but one or more of the person’s components, probably ib, or the sheut, or both. That would explain why the Ancient Egyptian characters we see in season five are in the Afterlife while their reincarnations are walking with the Earth.
It would also explain why Kaiba can read the text on the Ra card, but has no conscious memory of his past life. It could also explain why Yugi has such a resemblance to Atem (which suggests Atem is his preincarnation since that’s how these things work in anime): Atem is the akh that was trapped in the Millennium Puzzle, while Yugi has Atem’s ib/sheut."
Redditor /u/Captain_Kuhl has an explanation for why Yugi seems to be the only character whose deck isn't unified by a single theme. Since Pharaoh Atem (AKA Dark/Yami Yugi) held dominion over every tribe of monster when he reigned, he wouldn't have felt the need to align himself with any specific side.
Presumably, this sentiment carries over into modern times when he comes to possess Yugi Mutou. /u/Captain_Kuhl concludes:
"Yugi's first real deck was the one he received from his grandpa, who happened to be a firm believer in the heart of the cards (something he shared in common with the Pharaoh), and if memory serves, has precious experience with the ancient Egyptian civilization Atem ruled over. When you think about it, there's some halfway decent connections between the way Atem plays Duel Masters and his previous rule over Egypt."
In the Yu-Gi-Oh! anime, the toon monsters kind of come out of nowhere. Why do cartoon versions of select cards exist, and what is their purpose? Redditor /u/lunch77 believes the answer lies with Pegasus's desire for self-preservation. Since Pegasus was frightened by the capabilities of the Egyptian God cards he created, he needed a contingency plan in case they fell into the wrong hands. To defend against these all-powerful cards, he created new monsters that can break the rules of standard reality.
Our Redditor points us toward the toon monsters, who follow strictly cartoonish logic:
"Look at the qualities of Toon Monsters. Complete avoidance of being destroyed by battle. They can dodge any attacks from non-Toons, hide in the Toon World book, able to attack opponents directly, etc. Sure, Pegasus probably created the Toons, Relinquished, Thousand Eyes Restrict, etc. so that nobody could defeat him in a duel period but a lot of the cards seem to be an attempt to specifically counteract Obelisk, Slifer or Ra."