Yu-Gi-Oh! Monster Capsule GB is a Game Boy Color Yu-Gi-Oh! video game that was never released outside of Japan. It draws most of its inspiration from the manga's Monster World story arc and the Capsule Monster Chess stories, using both Duel Monsters and Capsule Monsters as game pieces.
After Death-T and Seto Kaiba's subsequent coma, the Millennium Ring saw potential in him and corrupted him. Set on revenge, Kaiba extends an invitation to Yugi and his friends to visit his Duel Tower. Once there, the Ring traps Yugi's friends and family inside RPG figurines. The only way to free them is to defeat Kaiba and his minions, the Dark Masters, and enter the RPG worlds and complete the storylines there.
Gameplay is a Turn-Based Strategy game similar to chess. Each monster has different stats and attacking ranges, which can be increased with items. Attacking is calculated by terrain and elemental advantages, whether or not an enemy can be attacked by more than one monster, and dice rolls — critical hits and critical fumbles can occur. When monsters are destroyed, they're lost forever, so players must choose battles carefully. In the RPG worlds, random encounters and some events are determined by dice rolls.
Yu-Gi-Oh! Monster Capsule GB provides examples of:
- Adaptational Villainy: Mai is working for Kaiba in this game, and keeps Tea's figurine trapped.
- Artificial Stupidity: The AI will sometimes move its pieces around or pass turns without attacking, even when attacking means it could win.
- Bragging Rights Reward: Yami Yugi's figurine can only be unlocked after training Yugi to the maximum level, and Yugi can only be unlocked if the player has rescued all of his friends. Yami has extremely high stats and can attack the entire field if you use a range-affecting item, but the sheer amount of effort needed to get him means that when you finally do not much can stop you to begin with.
- Brainwashed and Crazy: Kaiba's subordinates, and Kaiba himself, have been corrupted by the Millennium Ring.
- Broke Your Arm Punching Out Cthulhu: Using Exodia to win a match causes one of his pieces to disappear afterward.
- Broken Bridge: There's a literal broken bridge in Rex's tabletop world. You have to find a carpenter to rebuild the bridge to progress.
- Can't Hold His Liquor: Mokuba's world has you getting a bottle of liquor to get by some monsters, which instantly renders them unconscious.
- Class Change Level Reset: Evolving monsters drops their level to one.
- Continuing is Painful:
- Losing a battle when in an RPG World results in you getting kicked out of the tabletop game and forced to go through the story again. This also prevents you from rescuing all of Yugi's friends.
- If you win a battle but lose a monster in the process, that monster is lost forever.
- Critical Failure: Rolling a 95 or above will make your monster attack itself.
- Critical Hit: Rolling a 10 or below means a critical hit, with 00 giving you the highest damage possible for one.
- Demoted to Extra: In probably the only instance of Ryou Bakura getting more screen time than Yami Bakura, the Spirit of the Ring doesn't appear in person at all until after the game is beaten.
- Dismantled MacGuffin: Several items in the RPG Worlds are divided into three pieces, which you must collect and assemble to progress.
- Easy Level Trick: Seto Kaiba, the hardest fight in the game, can be rendered a Zero-Effort Boss if you bring a Dragon Capture Jar into the fight, which sucks up enemy dragons. Since his team consists of nothing but dragons, you can win without doing anything.
- Elemental Rock-Paper-Scissors: Monsters do more or less damage to one another depending on their elemental attributes.
- Escort Mission: In Rex and Mai's worlds you have to escort NPCs to certain characters. Thankfully, they're in no danger from monsters.
- Event Flag: These crop up in-story and are signified by a chime.
- Fetch Quest: Most quests in the later RPG worlds involve finding multiple pieces of an item or taking specific items to specific characters.
- Fire and Brimstone Hell: Seto Kaiba's RPG World is a literal representation of Hell, though only the first layer has fire. The second and third layers deal with lightning and darkness.
- Flawless Victory: Getting through an RPG World without a single Game Over is required to rescue one of Yugi's friends.
- Guide Dang It!:
- A specific wall in a single NPC town has an easily-missed weak point that indicates you can break it, revealing ways to continue to new areas and progress the story. This is never seen before or after this town, making it easy to not know how to progress without a guide.
- To unlock Yugi and Yami Yugi, you have to have beaten the game and have rescued all of Yugi's friends. At the tower's basement floor, you need to put 98 Star Chips into the machine to get Yugi's figurine. Then you have to train Yugi to Level 50 and use an Evolution Chip to evolve him into Yami Yugi, whose stats are rivaled only by the Blue-Eyes Ultimate Dragon.
- I Have Your Wife: Kaiba kidnaps Yugi's friends to force Yugi to play his games.
- Instant-Win Condition: Placing all of Exodia's pieces on the field results in an automatic win.
- Killer Game Master: Losing in the RPG World means Yugi's friends will stay trapped, and Kaiba and his followers are determined to defeat you by any means necessary.
- Magikarp Power: Some monsters are very weak at first, but can become very powerful if you level them up and use an Evolution Chip.
- The Man Behind the Man: Yami Bakura, who's controlling Kaiba, is the one behind his heinous actions.
- Non-Standard Game Over: While you generally get a game over if you lose all of your monsters on hand, you can also get a game over if you ante your only Star Chip on a duel and lose. Losing specific story duels (against the Puppeteer, Panik, etc.) will also cause a game over.
- NPC Roadblock: Some NPCs won't move until you either convince them to leave or find ways around them.
- Optional Boss: In the postgame, you can optionally duel Joey, Tea, Tristan, Ryou, Grandpa, Pegasus, Bandit Keith, Shadi, Yami Bakura, and a freed Seto Kaiba.
- Peninsula of Power Leveling:
- Mako's team gives out a huge amount of experience and can be used to reliably train once you get strong enough to outlast his monsters.
- In the postgame, Shadi's team of Yugi's friends gives high amounts of EXP with minimal risk to a party barring critical hits.
- Permadeath: Losing a monster means it's gone forever, though this doesn't apply to Yugi's friends.
- Permanently Missable Content: After you beat the game, you can't fight Weevil, Bonz, or Mako again, or go into the RPG Worlds. It's also possible to fail rescuing Yugi's friends, rendering them unavailable as figurines unless you start an entirely new game.
- Prison Episode: Seto Kaiba's RPG World starts with Yugi's imprisonment.
- Quirky Miniboss Squad: Mokuba, Weevil, Rex, and Mai are Kaiba's four Dark Masters.
- Random Encounters: These are decided by dice rolls and the number of steps you've taken—for instance, in Mokuba's world every 10 steps is a 30% chance to be attacked. Dungeons tend to up the stakes.
- Rule of Three: Progressing in later RPG Worlds often requires you to collect three of something.
- Save the Princess: Mokuba's RPG World storyline is a typical save-the-princess quest.
- Sound Test: There's a jukebox on the first floor of the tower that lets you randomly cycle through most songs in the game. Gameshark codes can allow a complete sound test, though it's prone to crashing.
- Spoiler Opening: The intro to the game reveals that the Millennium Ring has possessed Kaiba, something the characters don't learn until just before the final RPG World.
- Superboss: The postgame encounters with Yami Bakura and a freed Seto Kaiba have you battling the toughest monsters in the game.
- Talk to Everyone: A standard tactic to use when in the RPG Worlds is to talk to everyone, as doing so can trigger new event flags.
- Toilet Humour: While in Hell's dungeon, Yugi can find a bathroom with urinals but no toilets.
- Too Awesome to Use: Exodia's instant win condition at the cost of losing one of his pieces afterwards means you'll probably spend the whole game waiting for a fight big enough to use him on, assuming you can get the very rare pieces at all.
- The Vamp: Mai flirts with Yugi upon meeting him, to the annoyance of Tea.
- White Mage: This is Ryou Bakura's character archetype.
