- Bad Export for You: The Pocket Station features in the Japanese version were removed from the international versions, while the game's card drops weren't altered to account for it, thus rendering the many cards that could only be obtained from these features to be unobtainable without cheating in the international versions. Besides rendering 100% completion impossible, it also makee the international versions more difficult by barring the player from obtaining a significant amount of the more powerful cards.
- Early Draft Tie-In: The game itself is essentially a rough draft of the Ancient Egypt arc, with story beats remaining mostly the same but with different characters involved, and Marik and Thief King Bakura don't appear. Instead, Seto is a straight up villain and Kaiba holds the Millennium Rod in the present day, Ishizu is named Isis and is a fierce, antagonistic character with a water and dragon-based deck, and there's a God of Evil who created the cards and is summoned when all the Items are gathered, but is less openly destructive than Zorc.
- Game Mod: There's an active modding scene for the game with several mods available. The most basic mods make all the unobtainable cards winnable at extremely rare drop rates while leaving the rest of the game untouched. Other mods make these cards more reasonable to obtain while also substantially altering the opponents' drop lists, altering opponents' decks to be more faithful to the manga/anime and more difficult, and may have some other tweaks like changing the starchip cost for each card and adding rarity colors to cards' names to indicate their rarity. Then there are mods that make more radical changes, such as changing the opponents to new characters and altering the story, replacing cards with new ones, changing existing fusions and adding new ones to the game, and even adding monster effects into the game, while also tending to significantly ramp up the difficulty if you thought the original wasn't hard enough. There's also a modding tool and a randomizer available.
- Junk Rare: A card dropping from a single opponent with a drop rate of 2/2048 doesn't mean it'll be any good; in fact there are many cards that are this difficult to obtain yet are utterly useless beyond the early game. A good deal of the unobtainable cards are also weak-to-mediocre in stats and would only have use as basic fusion fodder.
- A particularly frustrating example are the Exodia arms; every opponent drops one of them at a rare rate, but since you can't get the legs without cheating, they're utterly useless, and they have a deck limit of 1 too, making the subsequent copies you'll inevitably get entirely unusable even if you did want to use them for some reason. Exodia's head is also a very rare drop that will be useless on its own once you can get it, but since only a couple opponents drop it, you won't be constantly taunted by getting useless copies like you will with the Exodia arms.
- Urban Legend of Zelda:
- There are many cards in the game that cannot be won from dueling. Naturally, there have been people who have claimed to have won these cards, usually in combination with claiming to having won it through having an extraordinary amount of wins against a specific opponent, as well as dueling in a specific, convoluted way. All of these claims were never verified, with their video/screenshot proof always being debunked. Eventually, a group of players hacked the game, and found that these cards are not in the drop list for any opponent. Even with this proof to confirm these cards as unobtainable, it hasn't stopped people from claiming to have won them or believing they can be won through some way.
- The prevailing theory for why the Meadow Mage has such nonsensically good card drops is that Yugi or Yami Yugi was originally an opponent in the game, who was then removed for whatever reason, while the drop list used for him was given to the Meadow Mage or the Meadow Mage's data was inserted over Yugi's without altering the drop list. The main point of evidence people point to for this theory is that many of the Meadow Mage's most common card drops are cards associated with Yugi, including the Dark Magician and Gaia the Fierce Knight at a common drop rate of 46/2048. There is no evidence in the game data though that suggests a form of Yugi was ever an opponent in the game.
- What Could Have Been: Word has it the game was created as a way to test out rules and features for the actual real life card game, hence why the play style is so different between the two. This includes the Guardian Star system, playing one card at a time, and the ability to fuse monsters without the need for a fusion card, as well as the fusions requiring general monsters of a certain criteria rather than requiring specific monsters.
- The Wiki Rule: The Yu-Gi-Oh! Wiki, and the forked site, Yugipedia.
Trivia / Yu-Gi-Oh! Forbidden Memories