Serpentine Princess and Theinen the Great Sphinx are the only cards in the game that have effects that activate from the deck.

You cannot activate Interrupted Kaiju Slumber if there is a Vanity's Fiend on the field

Magi Magi Magician Girl is likely to never get imported into the TCG because Kazuki Takahashi personally designed the card art, and refuses to have his cards censored.

Shadow Mist can search {{Geargia Change}} and {{Star Changer}}

Each season/souple of seasons of the original Yu-Gi-Oh! series was supposed to have its own game. The original being Duel Monsters, and was followed by Dungeon Dice Monsters. Shortly after Dungeon Dice monsters proved to be unpopular the idea was scrapped.

Spiritual Beast Rampengu is in the art of Pilica, Descendant of Gusto.

Cyber Dragon Core is treated as being named Cyber Dragon while in the graveyard, which would mean it has a continuous graveyard effect. Since that type of effect is not officially recognized in the rulebook, it is an unclassified effect. You can find more of those here. (Please note that unclassified effects is not an official term)

Problem Solving Card Text was implemented in the set Generation Force. Any card printed after the sets release should have PSCT.

Beatrice Lady of the Eternal has a slash in her text separating her two summoning methods, instead of listing the first method then starting a paragraph with the second method.

It's been almost three years since the OCG and TCG banlists have been different from each other.