Most of Aster/Edo's Destiny Heroes have names that start with D. Most of the cards' names were changed for the dub; Diehard Guy was renamed "Captain Tenacious."
As noted under Punny Name, Yubel's name may trace back to several forms: "juwel" (you-vel), meaning jewel in German; "jubel" (you-bell), meaning happy or joyful in the Scandinavian languages; or "übel", meaning evil. Yubel discovers that there is no happiness for her in being evil, and that her true destiny is to help Jyuudai to defeat the Light of Destruction, not to take him away from his new Scandinavian (or possibly German—the spelling inconsistencies make either a possibility) friend with a jewel-based deck.
Daitokuji may be foreshadowing/making references to the Society of Light arc (somewhat) and especially the Darkness arc. His line, "Everything in this world is born through one substance, which changes variably, creating the sky and earth." is what Darkness' "The world was born from a single card..." speech is based on. And his card, The Philosopher's Stone - Sabathiel foreshadows the final opponent of the last arc, Darkness, who is the representation of humanity's despair. The hermetic angel Sabathiel is the Angel of Saturn, a planet which symbolizes Nigredo. The Nigredo phase has been interpreted by Carl Gustav Jung as the period of despair.
When you keep that in mind, a lot of things about GX that initially made no sense or just seemed weird suddenly make more sense. For example, the community at tv.com found a lot of the Freudian Excuses ridiculous — Martin making a Deal with the Devil just because his parents got divorced, Fujiwara being overcome by Darkness and orchestrating Instrumentality just because his parents died... In retrospect, maybe they were supposed to look ridiculous and show how having some normal sadness or Parental Issues in your past is a lame excuse for causing The End of the World as We Know It. Even Edo thought him risking his life to protect Ekou made no sense — deliberately showing how absurd The Dulcinea Effect is? And, of course, there's Fujiwara needing to use Mind Control to get characters to Remember the New Guy and Manjoume's Break the Haughty arc going so far that it becomes detrimental to him. Basically, the more audacious and over-the-top this show's use of a trope is, the more likely it is that it's actually a Take That at the trope or its genre. ~Lale
I've noticed that whenever people reference Yugi in GX, it's always referring to Yami. At first, I thought that this was shallow, since it references solely his actions in the original series without taking in consideration the time gap between DM and GX. Later on, I had realized that this was Yugi—in the time span between the two series, Yugi had changed dramatically from who he was in the start of the entire series. His Yami-like appearance was an artistic representation on how he matured. This to the realization why his face is obscured during the present day—he does look like Yami, but hiding it blocks non-Brilliance'd viewers from thinking Yami might be back.
If You think about it The Entire reason that Yugi gives Jaden the "Winged Kuriboh" Card at the start of GX is because Yugi knew who he was, as well as the fact that he would use the Kuriboh cards because of the events of The Tenth Anniversary Film. This is because in the film Jaden uses The Flute Of Summoning Kuriboh. For Jaden, he is meeting Yugi for the third time, but for Yugi, they are meeting for the first time. (The order being "GX:1", "GX:180", "The Movie" for Jaden, but for Yugi "The Movie", "GX:180" "GX:1") This explains why Yugi would give a random duelist one of his cards, as well as why in episode 180, Yugi (the one Jaden duels, in the past) knows Jaden's name, without being told.
The names of the different groups were chosen by Kaiba which is why Obelisk is at the top, because it was Kaiba's god card. It also explains why Slifer is at the bottom, because it was Yugi's original god card and Kaiba doesn't like Yugi.
At first glance it seems like the dub names were chosen at random, but upon realization that Duel Academy is a prep school, all of the Preppy Names make sense
Before going to Domino City, Sartorius is coldly confessing to Aster that their friendship is only a part of destiny, like everything else he taught him, and Aster's purpose was served brainwashing members, Sartorius has tears running down his face. Strange for the Big Bad to be crying while displaying his Manipulative Bastard plan, but later on revealed Sartorius was under Demonic Possession by the Light of Destruction and it was the real Sartorius crying as the Light cut off his friendship with Aster.
Yubel is an exaggerated Violently Protective Girlfriend during Jaden's childhood because she has been the guardian of the Supreme King's vessel for several unknown lifetimes. Who knows what experiences Yubel has encountered trying to protect him from people pretending to earn his trust, or even considering the Supreme King himself can turn out to be evil, Yubel didn't take any chances with whatever Jaden or his friends might believe his best interests are.
In the fourth episode of the first season, Duel Academy has an entire military transport just to protect its shipment of rare cards. It's validated when the captain mentions they've had to fight off "mecha-triggers (something like that) and attack subs". People probably died. Considering the fights people get into using them, this is a world where wars may very well be fought over trading cards as weapons.
Take a look at the future Nightshroud shows Judai in their final duel after watching 5ds. Seem familiar?