IRL Lore
This card apparently practices the ancient Greek martial art "Pankration"
Dinowrestler Pankratops
When this card was originally released in the TCG, it was impossible to summon because the card needed to summon it wasn't out yet.
Blue-Eyes Shining Dragon
Originally a prize card in the TCG, this was once one of the most powerful cards in the game until it was banned and finally errata'd.
Crush Card Virus
Sacred Phoenix of Nephthys
Winged-Beast
This card is notorious for having only 1 TCG printing and because of how hard it is to tell when its unique effect can actually be used.
Mystical Refpanel
This card is named after the central text of Thelema, a religion founded by occultist Aleister Crowley
The Book of the Law
For some reason, this card was released in the TCG with the first Dinosaur Structure Deck.
Five-Headed Dragon
This card originally released as a video game promo, but saw brief use decades later as a hedge against hand traps.
Exchange
Loki, Lord of the Aesir
Spellcaster
In the Millennium World Arc, Yami Yugi becomes this monster in an attempt to destroy Zorc Necrophades
Black Luster Soldier/Dragon Master Knight
This card is named after a fossil that looked so weird, the person who discovered it thought he was hallucinating.
Paleozoic Hallucigenia
This card technically provides an alternate win condition, but was more commonly played as an extender in select few decks due to its level and Summoning condition.
Exodius the Ultimate Forbidden Lord
This card can be used to enable the Reversal Quiz OTK by activating its effect 19 times in the opponent's Standby Phase.
Inspection
Gladiator Beast Domitianus
Sea Serpent
In the Dark Side of Dimensions, Yugi uses this card in combination with Dark Magician to destroy Blue-Eyes White Dragon
Metamorphortress
This card's effect is a reference to the Golem of Chelm, which kept growing in size. It is named after the inscription on the golem that gave it life.
Emes the Infinity
This card first appeared in the manga with an extremely inappropriate name that was quickly corrected in the following week's chapter.
Dark Necrofear
This card's effect is useful, but even without it, it has utility as a garnet because of its name and type.
Neo-Spacian Aqua Dolphin
Pyrorex the Elemental Lord
Dinosaur
This was a pretty strong Trap Card for its time, but has a high activation cost, which was a source of significant drama for Yugi and his friends.
Horn of Heaven
Lord Cardigan's 1854 cavalry charge in the Crimean War led to 600 British casualties, and a poem on which this card is based.
Charge of the Light Brigade
In the TCG, this was the first DARK monster whose card text actually stated that it can't be Normal Summoned or Set.
MaZera Deville
This card is almost unplayable due to the fact that its own effect makes it impossible to play 3 copies of the card needed to summon it in the Main Deck.
Neo-Spacian Marine Dolphin
Guardian of Order
Warrior
Yugi only uses this card once in the anime, and he uses it outside of a duel. However, it is one of the strongest cards not only in his anime deck but also in the several TCG Yugi starter decks.
Dark Hole