Yu-Gi-Oh! Monster Capsule GB is a video game for the Game Boy Color. It has only been released in Japan. The game takes most of its inspiration from the manga's Monster World story arc and the Capsule Monsters stories, using both Duel Monsters and Capsule Monsters.
Seto Kaiba possesses the Millennium Ring and is captured by its power while his mind was shattered after losing to Dark Yugi at "Death-T". Kaiba then invites Yugi Muto and all of Yugi's friends to "Duel Tower". Once in the tower, the ring uses its power to transfer the souls of Katsuya Jonouchi, Anzu Mazaki, Hiroto Honda, Bakura Ryou, and Sugoroku Mutou. In order to get his friends and grandfather back, Yugi has to defeat Kaiba and his minions, the Dark Masters, in the "Monster World Tournament" using "Monster Capsules" (MC). Getting a Game Over in a world means Yugi will fail to rescue one of his friends.
The first floor's boss is Mokuba Kaiba, who's holding Joey captive. His RPG storyline is a typical save-the-princess quest; a village chieftain's daughter was captured by monsters and held prisoner in a cave. Yugi gets past the guards with the help of a bottle of sake and defeats the boss of the dungeon, rescuing the girl and Jonouchi as long as he didn't get a Game Over.
The second floor's boss is Weevil Underwood, who's holding Bakura Ryou captive in a dense forest. Upon entering the forest, one of Yugi's monsters is stolen by bandits, meaning he'll have to fight with a limited team. The bandits use Yugi's capsules as practice to summon a Great Moth, but their main goal is summoning the Perfectly Ultimate Great Moth using a sacrifice. Yugi rescues his capsules and defeats the Moth, saving the day and Ryo if he didn't get a Game Over.
The third floor's boss is Rex Raptor, who's holding Tristan captive. In his world, a water shortage causes a feud between two kingdoms. To mend the feud, Yugi must get to three aqueducts and bring water back to the parched land, going back and forth between the kingdoms as necessary. The final trial is the Two-Headed King Rex, who guards the final aqueduct, which is between the two kingdoms and accessed via a shrine. It chases Yugi back to the shrine for a final battle after several optional fights determined by dice rolls. Upon defeating it, peace is restored, and Yugi rescues Tristan as long as he didn't get a Game Over.
The fourth floor's boss is Mai Valentine, who's holding Tea captive. After flirting with Yugi, she directs him to a mountain, where an egg is being attacked by a Harpie Lady. Yugi hatches the egg and finds a Baby Dragon, who needs to become a Thousand Dragon before the entire land is wiped out by a volcano--complicated by the fact that a Koumori Dragon claims a Curse of Dragon has cursed Baby Dragon. To undo the curse, they must go back in time via a Time Wizard. Yugi successfully reaches the Time Wizard, but he refuses to help until Baby Dragon risks his life to save his son from a Harpie Lady. Yugi goes back in time, where they witness the Thousand Dragon losing a fight against Curse of Dragon. Yugi defeats him, but the curse is still in effect. The Koumori Dragon had revived Curse of Dragon, de-aged Thousand Dragon into an egg, and sent his Harpie Lady attendants to stop Baby Dragon. Yugi returns to the present day and confronts him. Upon defeating Koumori Dragon and Curse of Dragon, Baby Dragon successfully becomes the Thousand Dragon. Thousand Dragon saves the village from the erupting volcano, and Tea is also saved provided Yugi hasn't gotten a Game Over. He can also obtain Baby Dragon if he agrees to let it join him.
Before the player reaches Seto Kaiba, the boss of floor 5, Mokuba explains to Yugi that his brother had been acting weird since Death-T. Yugi confronts Kaiba and finds that Yami Bakura is controlling him via the Ring, keeping his mind shattered to further his plans. The only way to free Kaiba and save Solomon Muto is to complete the final RPG.
The final RPG begins with Yugi literally being dragged into Hell, which has three layers: fire, lightning, and darkness, each separated by a tower. Yugi must get through all three to return to the human world. He lands inside a prison, and the demons there enslave him, as well as his grandpa and the Dark Magician. Yugi escapes alongside the Dark Magician, whose staff has been shattered into pieces. Yugi finds the first piece in a tower, which is guarded by the Red-Eyes B. Dragon.
The second level of Hell contains a graveyard where the second piece of the magician's staff draws lightning to a rock. Yugi finds a substitute rod near a lava lake guarded by a Fortress Whale, then battles Pumpking the King of Ghosts in the graveyard to progress to the second tower. In the tower, Yugi finds the Dark Magician battling a Summoned Skull. Raising the magician's staff, Yugi battles the Skull himself, and they progress to the final layer of Hell.
The final layer is shrouded in darkness by the Castle of Dark Illusions, and to progress Yugi must assemble the Swords of Revealing Light and place them on specific rocks, guided by clues in a nearby dungeon. Once inside the castle, an Illusionist Faceless Mage brainwashes the Dark Magician, making him attack Yugi. Yugi defeats him and presses on, where he meets the ruler of darkness, King of Yamimakai. After defeating him Yugi meets the Blue-Eyes White Dragon, who will take him back to the human world if he can beat all three of them in a fight. Upon winning, however, the three Blue-Eyes combine into the Blue-Eyes Ultimate Dragon! When Yugi defeats it as well, the Blue-Eyes White Dragon agrees to take him back, and the Dark Magician repels a last attack by the King of Yamimakai and asks to join Yugi's team.
Upon Kaiba's defeat, Yami Bakura refuses to let Yami Yugi go even though he won, but Kaiba breaks free of his control, snapping the Ring's cord. Kaiba grudgingly thanks Yugi but promises to duel him soon, and all of Yugi's friends and family are freed in the storyline. If Yugi didn't get a single Game Over in Kaiba's world, he can use Grandpa's figurine in battle in the postgame.
In the postgame the player can duel Joey, Tea, Tristan, Ryou, Grandpa, Pegasus, Bandit Keith, Shadi, Yami Bakura, and a freed Seto Kaiba. The latter two have the toughest monsters in the game. Special capsule machines are also unlocked, and if the player saved all of Yugi's friends, they can unlock Yugi and Yami Yugi as figurines by putting in 98 Star Chips into the basement floor's capsule machine, then training Yugi until he's Level 50 and using an evolution capsule on him.
- Boss: Mai Valentine
- Capsule Machines: 2
- Boss: Seto Kaiba
- Capsule Machines: 2
- Official site
- The Cutting Room Floor page
- Data Crystal page
- The Spriters Resource page
- Japanese walkthrough and hint site