Seto Kaiba is one of the main characters in the Yu-Gi-Oh! anime, but he wasn't always a hero of the story. At times, he was a villain, a major roadblock to the group that Yugi had to overcome if he wanted to save the world, or whatever he was saving during that particular arc.
Whether Kaiba was a hero or a villain to the story at hand, he was always a big part of the plot. He also spent a good portion of said stories saving Mokuba from various kidnappings. Here are some times he did the right thing and some where he just made everything worse.
Right Thing: Rescuing Mokuba On Duelist Kingdom
Kaiba gave up just about everything when it came to saving Mokuba from Pegasus on Duelist Kingdom. Mokuba is just about the only character that Kaiba actually loves, so every time that he's kidnapped (which is often), Kaiba is right behind him trying to rescue him.
While he lost to Pegasus this time around, he did everything in his power to try and save his brother. He even went a bit too far at times, but given his brother was on the line it was the right thing to do.
Made Things Worse: Wouldn't Work With Yugi
During the Duelist Kingdom arc, Kaiba and Yugi were facing off to see who would get to enter the castle. Both duelists were fighting for a family member, and Kaiba was not going to lose.
When Yugi was close to winning, Kaiba forced his hand to win the duel. Had Kaiba and Yugi joined forces they may have been able to take Pegasus on and win, but Kaiba was determined to work alone.
Right Thing: Helping Everyone Off Of Duelist Kingdom
Of course, once the Duelist Kingdom arc was over, Kaiba was happy to help everyone off of the island to get back to Domino City. Yugi did save everyone, so it was sort of the least that he could do, but it was a kind act nonetheless.
However, the next time the crew was in an air-based vehicle with Kaiba, things weren't so good.
Made Things Worse: Letting Several People Fall Into Comas During Battle City
Bakura, Mai, Odion, Joey, half of the Battle City finalists were literally sent into comas during the end of their duels, and Kaiba refused to land the blimp to get them medical attention. Instead, they stayed in the on-board hospital and had to hope for the best.
Kaiba did this simply because he wanted the power of The Winged Dragon of Ra and Slifer the Sky Dragon in his hands, which is a horrible thing to do. He toyed with people's lives simply because he wanted power. This is easily one of the worst things he's ever done.
Right Thing: Facing Off With Noah
While Noah was a little brat that used Mokuba as a bodyguard to ensure that he wouldn't lose, Kaiba was originally the one who was going to challenge him to save everyone in the Virtual World.
While Yugi eventually had to be the one to save them all because plot armor, Kaiba was willing to risk his life if it meant that everyone else could escape. A sharp contrast to the Battle City finals.
Made Things Worse: Digging Up The Millennium Puzzle
Kaiba straight up desecrated the Pharaoh's resting place during the Dark Side of Dimensions movie. He dug up the pieces of the Millennium Puzzle simply so he could duel Atem one more time.
This was a very selfish thing to do. Of course, it does make sense to a degree. Atem was the closest thing that Kaiba had ever had to a friend. In the end, though, he made the wrong choice when he did this.
Right Thing: Working With The Group Against Dartz
Of course, when it came to the fight against Dartz during the Waking the Dragons arc of the show, Kaiba was on the front lines dueling for the fate of the world. Viewers have to give him credit for this one.
He also refused to let Yugi take on Dartz alone, and instead dueled alongside him in a tag duel during the final showdown. Without his help, it's likely that Yugi would have actually lost this duel, and the world would have been doomed because of it.
Made Things Worse: Overreacting When Yugi Lost His Title To Rafael
However, he wasn't always eager to help during that arc. When Kaiba first found out that Yugi lost his title as King of Games to Rafael, he became very upset.
While he eventually did come around, when the group first called him for help, he ignored them as he was far too angry at Yugi to even consider their request. If that isn't classic Kaiba, then really what is?
Right Thing: Offering To Be Yugi's Final Battle
When Yugi was trying to figure out who he would be facing off against during the Ceremonial Duel, Kaiba was quick to offer himself up as the chosen duelist.
While it always was going to be Atem in the end, it was very kind of Kaiba to offer himself up in the way he did. That was an act of friendship.
Made Things Worse: Constant Attacks On Joey
Kaiba never really respected Joey. Throughout the entire show he constantly threw jabs at him. While some were lighthearted in nature, a lot were actually pretty mean, especially in earlier seasons of the show.
He certainly didn't need to act this way all the time. Being a bit kinder to Joey would have gone a long way for Kaiba and probably would have made his time on the show more enjoyable and more full of company and friends.