History YMMV / YuGiOhTheFalseboundKingdom

** Any team combination with a special attack - the Dark Magicians with Dark Magician Girl, the Gemini Elves, the Battleguards, or Mai's Harpie Ladies. These special attacks consume AP from all monsters involved in it and use up their turn, but they deal heavy damage to the enemy team and can often KO them in two rounds, or at least leave them heavily weakened. Add in a third party member to heal them and/or restore their Action Points in longer fights, and there's no reason to just spam combo attacks each turn.

** Numerous duelists from Duelist Kingdom and Battle City appear as marshals, including Espa Roba, Mako Tsunami, Bandit Keith, Bonz, Weevil Underwood, and Rex Raptor. After they show up and join your forces, they spend the rest of the game just being portraits in your marshal menu, with no unique dialogue or impact on missions, even in cases where you can bring them to recruit their signature monsters, or the mission terrain is suited for their preferred king of card (for example, Mako joins up with Yugi ''after'' the mission where Yugi led his forces to cross the straight into the mainland.).

* ThatOneBoss:
** Arkana, especially if you did Yugi's campaign first. His Dark Magician is Level 99, and if you fight him as Yugi--[[SchmuckBait which he tries to make you do]]--he'll show off his Raigeki spells, which deal heavy damage to each of your monsters. To make matters worse, if Yugi loses you fail the entire mission. You could be seconds away from victory only to have to do it all over again.
** Scott Irvine's robot stand-in in Kaiba's campaign, especially if you already completed Yugi's campaign. You can only bring three marshals, and he rushes you with ''seven'' teams. Scott's own team is no pushover, as two of his monsters have 7 Blue Medicines and 3 Red Medicines, and all of them have a fair amount of Action Points and HP.
* ThatOneLevel: Yugi's campaign mission 15, "Betrayal," gives you about 30 seconds to reach Jakhud before Yami Bakura does. Fail to make it, and it's an instant Game Over. Only a handful of monsters in the game are fast enough to achieve this, and once they beat Bakura to the town, they'll have to defend it against Bakura seconds later. If you haven't been grinding up Harpie Lady or Ansatsu (two of your best picks to outpace Bakura), you're gonna have a rough time of it.

* LowTierLetdown: While Dragons tended to be the dominant type in other early Yu-Gi-Oh games, here they're easily the worst type. The crippling problem for Dragons is that they suffer from low action points, [[OneStatToRuleThemAll the stat that really matters in this game]], with most dragons having the minimum 2 AP at base and only going up to 4 at their max level. Then to make matters worse, Dragons don't get any equipment that boost their attack, so they won't deal as much damage per hit as other types will (and to add insult to injury, the only equipment they get, Dragonic Attack, makes it so they can't miss, while Spirits and Warriors get Silver Bow and Arrow, which does the same thing ''plus'' boosts their attack by 500 points). The only all-Dragon team that's worth your time is a team of three Blue-Eyes White Dragons with access to Polymerization, and even then they'll be heavily reliant on fusing into Blue-Eyes Ultimate Dragon to be productive, having too few action points to do much when out of Polymerization uses.

** While defending a base, you still have the option to retreat, but there's no penalty for doing it; the enemy marshal is still pushed back a short distance, buying you a little time. It's possible to exploit this by retreating constantly, stalling them indefinitely to let your party heal up more, to let base defenses charge, or to let reinforcements arrive at the base or take out the enemy's stronghold. The only risk is the escape attempt failing, which lets that monster without Action Points and the battle continues, but unless there's a significant difference in levels, this will rarely happen.
** Several monsters can inflict Paralyze with their normal attacks, letting them chainstun enemies for as long as they have Action Points. While the enemy's Action Points will remain since they can't take action while paralyzed, it's fully possible to KO them and render that a moot point.

*** Particular mention to Mai's Harpies. Aside from the three of them having a devastating team attack, they're the fastest monster in the field which makes them perfect for intercepting enemies or quickly seizing bases, and in battle they have good stats and a lot of Action Points, which will be boosted even higher if you put them on Mai since she has a very high bonus to AP. They also get two unique equip items that both boost their stats higher, and Electro-Whip lets them paralyze enemies with their normal attacks. The Harpie Ladies are one of the best all-around teams in the game, and with proper strategy can take out pretty much anything.

* DisappointingLastLevel: In both Yugi and Kaiba's campaigns, if you're expecting the final two levels to be the ultimate test of your strategy against an army of powerful foes, you'll be sorely disappointed. Because you're fighting [[spoiler:within the circuitry of the computer system itself]], all the paths in the last two levels are linear with a handful of bases between them, guarded by marshals that don't leave them. In the first, your monsters will end up just walking down a few hallways, beating the one stronghold blocking their path to the objective, and then move on to the final enemy, and the enemies you'll face aren't particularly powerful. In the actual final level, the final boss is right in front of you in a wide-open area, so you can surround the stronghold with your best teams and swarm it. There's not even a reason to drag the missions out, because the other strongholds in the area give a pitiful amount of money and have nothing of interest about them save for a single monster to recruit in Yugi's version.

* MagnificentBastard: Seto Kaiba is the CEO of Kaiba Corp and targeted by Scott to be drawn into the game. Initially acting as [[TheDragon head of Haysheen's guards]], Kaiba puts down rebellions against his rule but has no interest in actual being loyal to a virtual simulation. When he comes across Joey Wheeler and his Black Dragon Gang, Kaiba goads him into confronting him so his forces can destroy their headquarters, and [[AdaptationalNiceGuy actually acknowledges Joey's ability]] when he beats Kaiba. After Marthis frames Kaiba as a collaborator with the resistance, Kaiba [[HeelFaceTurn goes rogue]] and takes command of Pegasus' rebellion for real, and leads them to victory after victory. In his campaign he eventually leads a coalition of marshals to the core of Scott's virtual world and destroys it.

** Kaiba's campaign starts with Mokuba and Marthis as his allies, and Marthis leaves quickly. This could be a chance to explore the dynamic of the Kaiba brothers in a different dynamic, perhaps portray Mokuba as TheStrategist who comes up with plans, or have Kaiba mentoring his brother on how to handle himself on the battlefield. Nope - Pegasus joins very soon into Kaiba's campaign and he becomes Kaiba's NumberTwo, and Mokuba ([[DesignatedVictim of course]]) gets kidnapped halfway through Kaiba's story and doesn't return until close to the end.

* CheeseStrategy: While defending a base, you still have the option to retreat, but there's no penalty for doing it; the enemy marshal is still pushed back a short distance, buying you a little time. It's possible to exploit this by retreating constantly, stalling them indefinitely; you can use the time to let your party heal up, to build and charge base defenses, or to allow your own marshals to take out the enemy stronghold.

** Labyrinth Tanks. If they're the leader of a team, they move incredibly fast, and once engaged in combat they hit very hard and are pretty tough to take down. It usually takes a few rounds of combat in order to take down a team with a Labyrinth Tank.

** Fusion teams. Unless you can knock out one of the fusion components before they use Polymerization, you will almost definitely lose the fight or be forced to run.

** Dark Magician and Dark Magician Girl have a combo attack that does massive damage to all enemies. Both are gotten relatively early in Yugi's campaign and only need to be level 30 to use it. It works with any of the three Dark Magicians, meaning two of them on a team can spam it as long as there is enough AP. Notably, the other monster pairs with a combo attack aren't available until after Joey's campaign.
** Use Metalmorph on Red Eyes-Black Dragon and you will get Red-Eyes Black Metal Dragon, arguably the best all-around monster in the game. Its stats grow at an insane rate and it gains AP quickly. After a bit of training, you will have a flying tank that tears off massive amount of enemy health with each attack and is absolutely swimming in AP.
** Along with his Red-Eyes, Joey also receives his Panther Warrior early. Just like REBMD his stats and AP grow quickly and never slow down. While somewhat frail, his damage output and is easily one of the best in the game.
** Mai's Harpie Ladies get two unique equip items, both of them give them hefty stat boosts and the Electro-Whip lets them paralyze enemies with their normal attacks. The Harpies otherwise have good stats and a lot of AP, and if you put all three of them on a team they get a combo attack that deals massive damage to all enemies. Oh, and they're fast in the field to boot. The Harpie Ladies are one of the best all-around teams in the game and can take down pretty much anything with proper usage.
** If you play Kaiba's campaign first you'll get early access to one of Ishizu's monsters, the Dunames Dark Witch. Her abilities are better than most of the fusions monsters (Level-5 Magic, Status Guard, Lucky), and with the right equipment she can easily destroy entire teams by herself.
** Spirit Monsters are by far the most powerful type in the game. They have very good equipment and items, and many of them learn powerful abilities and specials as they level up. There's also nothing in the game that does extra damage against them.
** Both of the zombie monsters - Zombie Dragon and Armored Zombie - are Kaiba campaign powerhouses. With high attack and AP, and basic attacks that inflict poison and paralysis respectively, they stand with the best monsters in the game.

** Picking Kaiba's campaign first. Sure, he gets plenty of good monsters, but nothing compares to the magicians or harpies trios and they come at their starting levels regardless so you're much better off doing Yugi's campaign first so that they don't have to fight monsters around level 40 just to try and level up.

** As mentioned above, The Illusory Gentleman comes early at a high level. He gets even better later, gaining Level-3 Magic and a strong special attack. There's little reason to ever replace him.

** Give Mai all three Harpie Ladies, and equip each one with a Cyber Shield and/or an Electro-Whip. She now has a trio of monsters with tons of AP and a very high chance of paralyzing opponents, as well as a powerful special attack that hits all enemies. The Harpies are easily one of the best teams in the game in almost all situations, but especially when it comes to neutralizing enemies with items.

* ThatOneLevel: Yugi's campaign mission 15, "Betrayal," gives you about 30 seconds to reach Jakhud before Yami Bakura does. Fail to make it, and it's an instant Game Over.