The series revolves around people called duelists, who play a card game called "Duel Monsters". However, the villains in the series use the card game to invoke mystical and ancient magic duels called Shadow Games. Whoever loses a Shadow Game has their soul forever trapped in a magic void of darkness called the Shadow Realm.
A majority of the duels in the series revolve around the risk of being sent to the "Shadow Realm" upon losing. So there is still some sense of peril in the edited series, just not a lot.
Bakura is shown removing Pegasus' fake eye (as it is a mystical artifact). Nothing is shown however as the scene cuts away, but his scream can still be heard briefly.
A few characters fight throughout the series, although no punching or actual violence is ever shown.
Bakura is shown with a bandaged hand at one point in season 2, although he just says he was in an accident and spends most time at the hospital.
The last season is the most violent by edited means, as an ancient demon named Zorc is shown destroying ancient Egypt. Many buildings are in ruins and flames are scattered everywhere.
This is where the two versions differ the most, as all violence was edited out of the dub. In this original version, the Shadow Realm does not exist at all. Instead, if a duelist loses a Shadow Game, they actually die. This is even more disturbing since almost all of the duelists in the series are children or teens.
Several minor characters are killed throughout the series and even more risk the dangers of being killed. The villains are a LOT more menacing and sadistic. Characters (both main and minor) get into fist fights at times and punch each other or beat each other up. In addition, several main characters are threatened with guns and firearms throughout the series.
During the duel between Umbra and Lumis on a skyscraper, the loser falls to their death from the top of the building.
During the duel between Yugi and Arkana, the loser has their legs amputated with buzzsaws. Yugi wins the duel, but his darker side compels him to leave Arkana to his demise. He doesn't, however.
The villain of Season 3, Marik, wants to kill Yugi because he thinks he murdered his father.
Bakura stabs his own hand to create a convincing injury, thus explaining the bandage he mysteriously has in the edited version.
Bakura uses a card called "Ouija Board". Once it finishes spelling out the word "DEATH" after five turns, the opponent automatically dies.
In a flashback, Marik's father is shown mercilessly whipping his slave, Odion (the scarred flesh on his back is clearly visible). His father then proceeds to whip his own son after he tells him to stop. In an attempt to save their lives, Marik uses magic to pin his father against a wall and then stabs him to death with a dagger. Blood is shown on the wall as his father slumps to the ground dead.
Kaiba's kid brother, Noah, dies in the final battle against him. Mokuba later lays a white lily in the water in-memoriam.
During a flashback, Amelta's little brother is shown being sheltered by a tank. However, a KaibaCorp helicopter bombs the tank, killing his brother instantly. In another flashback, Rafael is nearly killed as a kid after a cruise ship he was on sunk. Everybody else aboard died, however he survived on an island only to escape and discover his relatives spent the entire fortune left to him by his family. He later digs up his parent's graves, not believing they're dead. However, he is later shown touching a human skull and cries in horror, holding the skulls of his parents in his arms.
The Winged Dragon of Ra electrocutes Joey, nearly killing him and sending him to the hospital.
Mai is later trapped by Marik in a magic sandglass and will die within 24 hours.
During the final battle against Zorc, in addition to the destruction, several innocent people and civilians are shown being killed in the chaos - including children.