Yu - Gi - Oh ! Monster Capsule GB 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 . Story . 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 .