These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The Zekrom that Nobunaga uses. You hear its roar on the title screen, it accompanies the Big Bad throughout the main campaign, and much is made of the battle leading up to fighting it. Ultimately, it's not much more difficult an opponent than any other in the game, and its Warlord even replaces it in a subsequent fight!
Demonic Spiders: Anything with Dragon Rage if encountered while your Pokémon's levels are still low. Which, unlike in the main games, is actually quite likely during some of the extra chapters (Ieyasu, Mitsuhide, and Nouhime all have a pretty big problem with this seeing as they start right next to Dragnor). On the flip side, this makes Ranmaru (with his Dratini) a Disk One Nuke if you manage to recruit him early.
Ensemble Darkhorse: Besides the usual Masamune and Yukimura (that might be influenced by other games), you got Hanbei, Gracia, Okuni and Motonari are popular among the fans.
Epileptic Trees: There's fan theories floating around that the game is set in the past of the main series canon, and the individual nations are actually the regions of the main games, or will become them after a geological shift.
Fan-Preferred Couple: The male warlord/Oichi and Yukimura/female warlord are quite popular. The former might have to do with the male warlord looking similar to Nagamasa.
Apart from the aforementioned Dragon Rage when Hit Points are still low, there are other examples. Fire Blast in particular is absurdly powerful: doing massive damage with an enormous range (it hits an area in the shape of the 大 kanji, i.e. "A plus shape in front of you and two squares on either side of you" according to Serebii) while not suffering from the poor accuracy it has in the main series. Only two Pokémon get it, but both of them (Emboar and Darmanitan) have massive offensive stats. Then again, given how long it takes to evolve the two that far, it may qualify as Last Disc Magic... until you transfer those Warlords over to another story.
There's also chance the very first Warrior you recruit will have Darumaka (which is quite good Pokémon itself for early game, especially if it gets Run Up)
This makes Kai one of the harder warriors to defeat given she gets Darmanitan and her power increases her speed (allowing Fire Blast to hit) and will probably cause your opponent to flinch, so even if you survive the fire blast, your lose a turn for flinching.
If you're unfortunate enough to be against an enemy Dragon with Outrage, run. Outrage is strong enough to kill almost anything that isn't a Steel-type, and hits all four tiles adjacent to the user. It's drawback is that the user can't move next turn, but they can still attack again. This makes any Pokémon with a melee attack doomed to a quick and painful KO, the rest of them will be able to get in one attack out of Outrage's range, but next turn you'd better run. And of course the user is a Dragon-type, so it resists several elements and has high HP and defenses. If the Outrage user is on the attacking side, you have the grace of being allowed to avoid them and run out the clock, but if they're the defender...
Some of the upgrades Warlord Powers are pretty powerful too. Hanzo's (increased movement and critical hit ration for your whole squad) can really make a mess of things... if you're lucky.
A lot of the game's difficulty snaps cleanly in two if you load up your team with Pokémon that are Flying-type or have the Levitate ability. They're able to move across any type of terrain freely, can move over other Pokémon, can move obstacles, and can even move across empty tiles as long as they move to solid ground when you end their turn. A good half the maps in the game become incredibly easy when your Pokémon can casually fly over impassible ground. Pugilis, where the entire gimmick of the kingdom is that when attacked a Pokémon is knocked off the central platform, becomes embarrassingly easy because your Pokémon that just got knocked off can simply fly back up and return the favor to their attacker.
Also, the Guardian Charm equip item. It can be bought from one of the traveling merchants (who show up infrequently) for 10,000 gold. It gives a significant boost to your Pokémon's stats if it's the only Pokémon remaining. While it was probably intended as a last hope if your army's been slaughtered, it also makes soloing incredibly easy. And like everything else that merchant sells, it stays with you if you start a new chapter.
Speaking of the traveling merchants, the financial curve can be shattered pretty quickly if you're good at gathering gold. Most of the items sold by the 'weird old man' and the 'pretty cute merchant' carry over between stories (Bulbapedia has a full list). By spending all your gold on traveler items before changing stories, this essentially allows you to carry over a fair chunk of your finances. note Since the merchants don't do Charisma bonuses, selling things directly to them will only net you 50%. However, if they appear on a given month, they will appear on that month regardless of resets; Save Scumming can net you up to 80% via ordinary Shops and 100 points of Charisma.
The Legendary Pokémon are hard to track down, but they are worth it. As you'd expect, they have high stats, long ranges, high HP, and powerful attacks which can hit multiple enemies at once. And once you give them the Guardian Charm, they will redefine the phrase One-Man Army.
Rank II Warlords often have ridiculously powerful abilities, several giving the entire team, regardless of position, instant stat buffs. Ranmaru ensures three turns of all allies never missing with their attacks, Okuni gives an instant Attack and Energy boost to the team, Yoshihiro gives a three-stage Attack boost to all allies in exchange for three stages of lost Defense, Shingen gives three turns of increased Attack and Defense. Ginchiyo and Muneshige both have abilities that give all allies increased Attack and Range, and they double in effectiveness if the other of the two used their ability in the same turn, allowing for all allies to have +3 Range and +3 Attack.
Genius Bonus: Rife with nods to real-life feudal Japan, naturally.
The Recurring Boss, Hideyoshi, is fought the second time as an assistant Warlord to Nene, the Poison-themed Warlord. While it is not mentioned in-game, him showing up for this one random battle out of the four available ones becomes a lot less random when you learn that Hideyoshi was Nene's husband in real life.
The first castle you conquer, Ignis, is ruled by a warlord specializing in Fire types. Ignis is Latin for "fire". Many of the other nations have Meaningful Names like this too.
Mitsuhide's special episode has him betraying Nobunaga, just like he did in real life.
A more minor one but Masamune's appearance is Eyepatch of Power might seem like a generic look until you realize that Masamune in real life is blind in one eye hence why you never see his other eye. Might double as a Fridge Brilliance.
You can see the eyepatch if you look hard enough. It's more noticeable in certain animations though.
The conflict between the kids Mitsunari, Kiyomasa and Masanori make more sense when you realize the three of them did not get along in real life and spent most of their time fighting each other. Made worse when Hideyoshi died and their fight escalated and implied that Mitsunari won hence why you play his chapter first (and why he's got a freaking SCIZOR)
Hanbei is an ill boy based on his real life counterpart and as a result, his coughing fits make a lot more sense when you realize how he died in real life.
This also explains why he doesn't gain that much power.
Why does Shingen always carry a paper fan around? It's a reference to a legend stating that once, when Kenshin attacked him with a sword, Shingen used a paper fan to defend himself.
Ina's abilities always allow her to hit her target. In Samurai Warriors, she's the archer, so of course accuracy is important to her as well as judging the distance between her opponent.
At the end of Okuni's story, she disappears and is never heard from again. This is based on her her real life counterpart disappearing without a trace and no one knows what happened to her after that which leaves to speculation on how her life ended.
Oichi and No have the highest charisma when you have them in your army. It makes sense for No to have a high charisma given the type of person she is, but why does Oichi have a high charisma? In real life, Oichi was known for being the most beautiful woman in Japan (that could rival No) and everyone sought her out. Ironically Nobunaga thought she was too tall for a woman and dismissed her hence why in this game, he doesn't congratulate Oichi on winning the beauty contest contrast to Ranmaru. When promoted, Oichi has a higher charisma than No by one point implying that as much as No wants to think of herself as the most fairest of them all, the title will always go to Oichi.
This also explains why Okuni has the third highest charisma for female warlords. Like No, she's very manipulative and in order to get her male harem, she has to appeal to many men.
The various generic warriors are named after figures in Japanese history/Samurai Warriors games, with a interesting note being Dosetsu who has the same perfect link line as his leader, Ginchiyo. In history Dosetsu was the name of her father and he passed down his sword to her. Except in this case it's a mon preference.
Ho Yay: Between Nobunaga and Ranmaru as shown in Ranmaru's episode where Nobunaga doesn't seem to mind the idea of Ranmaru being labeled as a woman and came all the way from his nation just to graduate him on the title. It makes sense given that in real life, they did have a sexual relationship.
Padding: Some of the post-game episodes have you doing things like befriending 100 Pokémon as your only goal. Borders on Fake Longevity with some episodes being the same scenario as others, just with a Perspective Flip. (Though sometimes this is still enough to make for a very different experience, such as with Mitsuhide and Motochika's episodes).
The Scrappy: Many people don't like Yoshimoto given his appearance, the fact that he's the only historical character to get worse instead of better, his story serving no real plot to his character development and being a Joke Character when he promotes. In fact, he's the only character that doesn't Took a Level in Badass when he promotes as his special ability causes problems to others and his Fortress can only do 1 damage given that the move is Gyro Ball.
Scrappy Level: Spectra's arena is widely hated. There are purple flames that move every turn and, if they move onto your Pokemon (Which they will do if they can), inflict a random status condition. Additionally, each turn, the numerous Misdreavus statues slide around, and they have an annoying tendency to park themselves right in front of you or block you off from advancing toward the enemy entirely. As if that wasn't annoying enough, the actual animations for the flames' and statues' "turns" are long, meaning that it's a long, boring time before you can move again. It's not a particularly difficult map, just very tedious and annoying.
The Gabite warrior in the post game that shows up once the game thinks you're "too powerful" for the AI. The Gabite warrior goes to one or two random nations and tells them to fight harder drastically increasing the level of the warlords and warriors of that nation by a large amount. It wouldn't be a problem given your strongest team is probably a little lower than theirs but the computer always attacks the nation with a low level in order to get even stronger than you, so unless you have promoted warlords or full evolved Pokémon, whatever warlord got the boost will end up preventing you from completing the episode quickly. Also, for the low level team, pray that the nation they attack is a collect the flag nation given that if the enemy is too strong, you could always hold the line and gain points allowing your stronger army to defeat them.
Pokémon and Warriors are not registered in the Gallery until you use them in at least one battle. This isn't a big deal for Pokémon, because even if you, say, don't use your new Weavile in battle, the Warrior will have it in every subsequent storyline. Where this is a big deal is that it does not register Warlord transformations unless you use them in battle post-transformation, so if you go through all the trouble to get a Warlord to Rank 2, then end the storyline without using them, the game will not give you credit for the transformation, and in subsequent storylines they return in their base forms until you have to do it all over again to register them this time.
Technically, evolving registers Pokémon as seen. However, to register it as owned (and have full information on it), you need to use it in battle and then win.
Confusion. In main series, it just gives a chance for Pokémon to hit yourself (which seems to vary) but here? It seems that confused Pokémon sometimes will move on its own. If you're cornered (sometimes by damn confusion itself), it can as well do nothing, wasting its move.
That One Boss: Mitsuhide in the main story. Mostly due to the annoying Frictionless Ice you have to cross, which pretty much works like the Ice Path in Pokémon Gold and Silver except you can only move once per turn, and it makes getting into range of your attacks really difficult. Flying Pokémon can ignore the ice, but guess what they're weak to, and what every enemy uses... Oh, and one of the generic enemy warlords has a Munna with a nasty habit of putting all your Pokémon to sleep. The Munna is also levitating, so it ignores the ice. To top it all off, Mitsuhide himself is no slouch; his Lapras is decently bulky and is equipped with the Awesome yet Practical Ice Beam (an attack that hits everything in a three-square line, has near-perfect accuracy, and is adequately powerful, to boot).
Ina and her Water/Ground-type Quagsire, by most cases. If you don't have a decent Grass type taking down her Quagsire can be a real pain (if you plan on recruiting her and do not have Motonari and his Grass-types, prepare to play around) especially given its not-to-be-sniffed-at Defenses. Also, its Ability reduces Range, and her Ability means that it won't miss.
Whichever Warlord gets a boost from the Gabite warrior in the post game becomes this especially when you're trying to unify Ransei.
Nobunaga starts with two powerful Dragon types in his army, inhabits the Dragon Kingdom and is one of the most aggressive AIs, meaning he can often conquer half of Ransei just as quickly as you can in the postgame. And he'll often recruit Warlords like Mitsuhide, Tadakatsu and Kenshin along the way.
You, the player, in any Warlord's episode that takes place chronologically after the main story. The hero(ine) is the only Warlord to maintain Rank II while controlled by the AI, which means that they also maintain their Rank II Warrior Skill, Courage. Put that on their unevolved Eeevee, and that's a two-stage Attack boost and a two-square Range boost on a four-square Range Pokémon with Celebrate, which allows you to move again if you KO a Pokémon. If you don't have any good allies, you can kiss your Game Breaker goodbye.
That One Level: During the main story, Pugilis. Oichi even notes when you choose to attack that her Jigglypuff and your Eevee are weak to Fighting-type moves, and guess which two Warlords you need to take to every battle? Nintendo at least acknowledged the problem and included with the game the password to send Dratini flocking to a random kingdom under your command.
Kiyomasa and Masanori's post game episodes might count. When you play as Mitsunari, it's very easy because he has a Scizor that can destroy the competition easily. When you play as Kiyomasa though, you can't do that much damage to Mitsunari but can take out Masanori easily, but that means having to wait for a Pokémon with a fire move to defeat Scizor or at least have a warlord with a Pokémon that can resist bug move. Made worse with Masamori as he can't do that much damage to Kiyomasa and he can't even harm Mitsunari with his Skorupi and you'll have to wait around until you get a Pokemon that can even hope to harm Scizor. And they say the difficulty of their chapters is one?
Oichi's post-game episode. Her army starts with normal-type Pokémon. Her neighbors include No's Ghost-type faction, and Ranmaru's Dragon-type faction of Disc One Nukes.
Mitsuhide's post-game episode. The usual post-game-chapter-strategy of attacking an army and recruiting them at the same time to boost your forces totally does not work, as all the nearby kindgoms are all controlled by Nobunaga. And you can't even sit still and recruit followers on the first month, as by February, Nobunaga would have stacked his border towns with powerful defenders.
Motochika has it worse than Mitsuhide. At least Mitsuhide has the type advantage on Nobunaga's Hydreigon and his Lapras gets an energy boost whenever it fights Hydreigon in this story only.
Motochika actually has it a little better than Mitsuhide, since he can at least rally together every Warlord from Fontaine to Chrysalia.
Masamune's level is intended to be difficult for those who jump into the level and not leveling him or Magoichi up. He starts in Avia surrounded by warlords that will either recruit quickly or have a type advantage over flying type. Conquering the top portion is difficult (but necessary to avoid the Gabite warrior and other aggressive AIs) because you're dealing with Misuhide (ice), Ieyasu (steel), Nobunaga (dragon but it's mainly because of Ranmaru being a Disc One Nuke for him), No (ghost and tends to recruit Warlords very quickly), Nene (poison that can defeat Magoichi very easily), Ujiyasu (rock) and Kenshin (psychic but Aya has an ice Pokémon). The worse part is that Masamune can only promote in his chapter so you'll either stuck with a Rufflet that can be defeated easily or a Braivary that ends up taking two turns to attack (and can result in the failure of recruiting some warriors) unless you use other flying Pokémon that can only be at 90 link.
Yoshimoto. Oh, by Alpha, Yoshimoto. Your objective is to recruit forty Warriors. Sure, Ujiyasu did the same thing a couple stories ago, but several things make this multiple times harder than the Cragspur scenario:
Shingen and Kenshin both control three kingdoms, splitting Ransei in half. This leaves you with four kingdoms to recruit warriors from, one of which is your player character (see That One Boss above).
Your only adjacent kingdom not controlled by Shingen or Kenshin is Violight, home to Ginchiyo and her husband Muneshige. You won't last ten turns.
Yoshimoto has nothing going for him in the Warrior Skill department, considering Deep Breath hinders your movement severely. Even Brave Bird and Volt Tackle give you a little bit of breathing room with one space to back up, but this sucker will leave your Pineco ass right in the middle of enemy fire with no way to move. Grace isn't any better, since it puts your entire army to sleep!
That One Sidequest: Getting your Warlords to Rank 2 is time-consuming and there's a bit of Guide Dang It, but if you know the circumstances needed it isn't too hard for most of them... but there's exceptions.
Shingen needs a 75% link with his Perfect Link, which is one of the higher amounts. The major problem is that his Perfect Link is Rhyperior, who can only move two squares a turn, and its attack is Rock Wrecker, which hits one tile three squares away, is highly inaccurate, and oh yes, has a recharge time. For most other Warlords, soloing a few rounds of wild Pokémon with the Guardian Charm on will get you up 10% or more. For Shingen and Rhyperior, it's a giant pain in the ass even with the Charm on. It's actually far easier to get him a Rhyhorn, grind its link level up without evolving it, then do so once it's at 75%.
Nene needs to have every Poison-type in the game registered in the gallery to upgrade. Better go get searching and grinding, it'll take a while.