Before its official release in the card game, there was another version of the Seal of Oricalchos but there were only 15 in the entire world, used in a single special tournament by Upper Deck employees where players could duel them. And yes, their version was just as overpowered as it was in the show, which is why the legal version got nerfed.
Along with the (nerfed) Seal of Orichalchos, the Legendary Dragons are released but as regular Spell Cards.
Chaos Sorcerer was nicknamed "the poor man's Chaos" due to its Common rarity, as opposed being Secret Rare like the Envoys.
"Boss Monster" is often used to refer to any particularly powerful monster that's tied to an archtype and has a powerful effect that makes dealing with it difficult, as well as being difficult to summon and often requiring cards from said archtype to even get it on the field. Naturally, true to the name, once it's on the field, it feels like a Boss Battle trying to get it off the field.
"Solitaire decks", for decks that focus on winning turn one and not even letting the opponent get a chance to play. The name comes from the fact that, since the deck is so focused on winning turn one and not letting your opponent get a chance fight back or even play a single card that the person using it might as well be playing Solitaire instead of Yu-Gi-Oh.
"Beatstick" is often use to describe monsters that have a high ATK stat, are easily summoned, but don't have any outstanding effects. (or no effect at all, in the case of normal monsters)
"Trish" for Trishula, Dragon of the Ice Barrier. Partly to keep its name short, mostly because people have found it fun to treat it as a female.
When decks are mixed together, they often take the suffix from one group. All Shaddoll variants end with 'dolls,' (ie, Shaddolls + Plants become Plantdolls, Trains + Shaddolls become Traindolls), Lighsworn variants end with 'sworn,' etc.
Performages and Performapals are an exception to this; they're called Performages & Pals. Also called EM-Em among Japanese circlesnote This is because Performapals are called Entermates in Japan (abbreviated as EM) and Performages are Entermage (Em), and Pepe among English-speakers. The latter has become the most popular.
Komoney has been picking up steam after the ban list where Konami not so subtly killed off all the major competitive archetypes of the early Arc-V era. It's now used frequently whenever Konami does something that blatantly "encourages" people to buy new archetypes.
"Pot of Stupidity" for Pot of Cupidity, since the downsides of the card greatly outway the pluses of it, and as such you'd have to be stupid to try and run it any deck.
The particular style of outfit Dark Magician wears has inspired an entire archetype of Magician cards, and of course he has many evolved forms.
In a roundabout way, it's now tradition for the protagonist's key monster to have 2500 Attack, while to parallel the Blue-Eyes, their rival's key monster has 3000 Attack.
Dark Magician Girl. Let's see: Magician's Valkyria, Gagaga Girl, Performapal Trump Witch, and Card Ejector.
The mighty Blue-Eyes White Dragon: Cyber Dragon, White Night Dragon, Red Dragon Archfiend, and especially Galaxy-Eyes Photon Dragon, most of which are played by major rivals and have equivalent attack and/or triple-fusion or Xyz variants. See below.
And for Blue-Eyes Ultimate Dragon, we have Cyber End Dragon, and Neo Galaxy-Eyes Photon Dragon. (Though the latter differs in that it is a triple Level 8 material Xyz monster.)
One can think of Red Nova Dragon as a Expy to BEUD as well considering that just to summon Red Nova takes two Tuners, meaning he usually has 4500 or more attack.
Franchise Killer: Allure Queen and Dark Lucius are believed to be the cards that finally murdered the LV archetype - Allure Queen for being too underwhelming in even its LV7 form, Dark Lucius for having its LV8 form be the only worthwhile form, and both for completely losing their effects if not Summoned using their lowest form, making Summoning either a slow (and often Unwinnable) grind.
No Export for You: The Anniversary Pack artwork for Dark Magician Girl was not included in the TCG release. According to most sources, this is because Kazuki Takahashi refused to edit the art for release outside Japan.
Additionally, the english pack did not get Duelist Pack: Kamishiro Siblings, and none of the cards from that pack have yet to be printed in English.
2ch users created a hoax so convincing, it tricked Japanese Yu-Gi-Oh! fan sites. The hoax basically stated that Lightsworn were dolls who were slaves of an evil force. This describes the Shadolls perfectly.
Prior to the official release of Primal Origin, there were sources depicting Starduston as a fake Duston version of Stardust Dragon. It also had a effect highly reminiscent of Stardust Dragon: During either player's turn, when a card or effect is activated that would destroy a card(s) on the field: You can Tribute this card; negate the activation, and if you do, destroy it. You can only control 1 face-up Starduston.
Konami got Kazuki Takahashi to do some artwork for several of the most iconic cards in the game. This included a very well drawn Dark Magician Girl card. However, when they requested that he make some changes to his art for an American release(specifically, toning down her cleavage), he refused. As such, there was no American release for that card.
According to the Duel Art artbook by Kazuki Takahashi, Magi Magi ☆ Magician Gal was originally intended to be simply another "Dark Magician Girl" art to act as a female counterpart to the anniversary art of "Dark Magician." It was later made into a new Xyz monster.