Yu-Gi-Oh! is currently in the midst of its fifth series, and despite the production problems the series is currently facing, it has a huge following that has been building up over its tenure. But it's currently much different than when the series first began.
The Yu-Gi-Oh! series was much darker before the series became more focused around its central card game, Duel Monsters. The beginning arc of the manga was later aluded in the anime, but fans in the West wouldn't find out they missed out on a whole slew of content from the Japanese original.
Toei Animation once produced a 27 episode anime adaptation of this darker, pre-Duel Monsters content. This was dubbed as 'Season 0' by fans, and featured a pharaoh that often played deadlier games of chance with foes, such as knife games and one where he set his opponent on fire. This first season of the series also had many characters and ideas that weren't seen in any other adaptations since the Duelist Kingdom arc (and subsequent Duel Monsters focus) was eventually adapted and licensed by a different studio.
Toei Animation introduced many original elements separate from the original series, such as taking a one-shot character and making her a main character in the series, and was thus deemed unpopular by fans in Japan. Shortly canceled thereafter, the series was then produced by Studio Gallop and became the series fans in the West know today.
In the United States, the series was dubbed by 4Kids and although it carried elements from the original adaptation such as the death games, the dub changed these to "Shadow Games" that became more about the abstract loss of a soul than the brutal taking of a life.
With the current all age friendly image Yu-Gi-Oh! has now, it's definitely hard to imagine it back when it was a lot darker in tone.
For those unfamiliar with Yu-Gi-Oh!, the series was originally created by Kazuki Takahashi. It ran in Shueisha's Weekly Shonen Jump from September 1996 to March 2004. The series follows Yugi Mutou, a young boy who solves an ancient puzzle and is possessed by the spirit of the Egyptian pharoah. Being skilled at deadly games, the Pharoah goes on to create and solve problems for Yugi based on deadly games of chance.
Two anime series were created for the series, but the one most fans will recognize is Yu-Gi-Oh! Duel Monsters. Yu-Gi-Oh! Duel Monsters was the first arc in the story to focus on the "Duel Monsters" card game and was the first season licensed for an English language release by 4Kids Entertainment. The first season of the series, which fans often dub as "Season 0," was more focuses on deadly games of chance with horrible consequences. It's a darker season of the series featuring many changes from the series' identity later on.
The currently running series, Yu-Gi-Oh! VRAINS, is the fifth version of the series following Yu-Gi-Oh! Arc-V and started airing in 2017. It takes place ten years into the future, where Duel Monsters is played through virtual reality tech as a young boy named Yusaku who is dueling to defeat a mysterious hacker group.