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.
Badass Decay: Bowser X, the Bonus Boss for the last game had a lot of HP along with many unavoidable attacks. This game, since Bowser is an early-game boss, Bowser X is easily curbstomped with a Luiginary Work, assuming you fight him later on in the game.
Justified in that you're fighting powered-up memories of the real Bowser as he was at that time. The real Bowser ends up averting this by hijacking the endgame.
Base Breaker: Antasma. Some fans of this game prefer him over Bowser by a longshot and would've much preferred him to be the final boss instead of Dreamy Bowser. The fact that he has arguably the best battle theme in the whole game helps. Others criticize him for his rather lacking characterization for a Mario RPG Big Bad. And people who find him Rescued from the Scrappy Heap upon finding out that he's not the Big Bad meet opposition from people who preferred him over Bowser (and thought he was gonna be the Big Bad).
Bowser also has this status. Some fans are happy to see him as a powerful and somewhat intelligent, Badass, menacing villain once again. Others criticize him for betraying potential new fan-favorite villain Antasma and hijacking the plot from him, and believe that such portrayals of Bowser should be confined to the main series games rather than the RPGs. There's also the fact that Bowser has lost his humorous Ineffectual Sympathetic Villain portrayal from his other RPG appearances in exchange for straightforward villainy.
Best Boss Ever: For regular battles, Wiggler and Popple, Bowser Jr, and Dreamy Bowser. For Dream World battles, the Elite Trio, Kamek and Antasma. For the giant battles... Well, if you don't hate them, it's agreed that they grew the beard with Earthwake, with him and the later ones contested for being the best.
Breather Boss: Antasma is somewhat easy compared to Giant Bowser before and Dreamy Bowser after. This makes sense from a narrative standpoint, considering you fight him right after Bowser hijacks the plot from him.
If you can count them as a boss (based on the music), then the Fly Guy R thieves are this. They're just normal Fly Guy Rs. No new attacks or gimmicks, and no more health or higher stats than usual. And you've beaten up dozens of them already.
Possibly Bowser Jr. He's not super easy, but his attacks are also not that difficult to dodge, especially compared to those Bowser X in the last game. He's a fun boss to fight though, so one could say he's the one example of a Bonus Boss ever who's actually legitimately entertaining to battle and isn't just ridiculously hard for the sake of being ridiculously hard. And then there's the Catharsis Factor.
Popple is fought right after beating the Wiggler; in the exact same fight, nonetheless. He is much weaker than the Wiggler and has one easy to dodge attack, so he shouldn't put up much of a fight.
Breather Level: The entire Ultibed quest, at least in terms of the part finding. Mini games, basic enemies, already visited areas, not much that's actually difficult in the slightest. Which is nice, considering it comes right after Driftwood Shore and its dream world, and right before Wiggler, Popple, Dreamy Wakeport 2, Earthwake and Somnom Woods, all of which are much more difficult to beat.
The Dream's Deep portion of Dreamy Pi'illo Castle however can be a headache, especially the fake Coin Block enemies that are tricky to dodge.
Broken Base: One of the most heated debates going around is about which game has a better final boss theme, this one or Bowser's Inside Story, believe it or not.
Catharsis Factor: Admit it: Chasing down Bowser Jr. by hijacking his Clown Car when he's out of it is immensely satisfying! The fact that it's an inversion of how things usually go when a chase sequence is initiated is the icing on the cake.
Fighting Popple, who Took a Level in Jerkass for this game, is also immensely satisfying despite (and perhaps because of) being incredibly easy. It's really too bad that he's not in the Battle Ring.
The absolutely epic Final Boss theme - Adventure's End, possibly Bowser's most emotional and haunting boss theme in the entire franchise.
Demonic Spiders: Cocoknights (and their R equivalents), Mechakoopas and Beehosses. They've all got at least one attack that's infuriating to counter, fairly decent stats and come in large groups in the endgame. Have fun.
Ensemble Darkhorse: So far, the Massif Bros (with their random beef references and muscle obsession) seem to be the most popular new characters in the game, and one of the things even some of the more harsh critic reviews call hilarious.
Even Better Sequel: Many people are in agreement of this game being the best game in the Mario & Luigi series, surpassing Bowser's Inside Story and even Superstar Saga.
Critical Dissonance: It's actually the worst-reviewed game in the series, but still positively reviewed nonetheless.
Birthday equips. These multiply a stat by 400% on your birthday (as set by the 3DS clock). Keep changing the date and you've got a ridiculously overpowered set of gear that can smash through anything.
Time freezing badges. Combine the Gold Badge and Miracle Badge, and you can stop time. And store the effect to use in any battle in the game. And use ridiculously overpowered attacks like the Zee Egg and Star Rocket twice before the enemy can even move. And then use the same effect again the second it runs out, for a max of four times in a row - or a whopping five if you time the Badge Meter's charging just right. Oh, and the Birthday equips stack on top of this. End result? You can literally do up to 50,000 damage before the enemy can even move or attack. It means you can take out the final boss before it can move, the penultimate boss before it can move and all four of Kamek's clones/forms before they can move. Oh, and it's possible to get this combo right before the final dungeon and literally steamroll through every boss in sight. And in the Battle Ring, the turn count does not move forward when this badge is in effect.
The POW Up+ rank bonus, which gives one extra POW point per level. While this may not seem like much, since damage and power do not have a linear relationship (try fighting some of the first enemies fought while at a high level), soon bosses will be defeated within a few turns.
The Wellington/Farmer's Boots. What does this pair of boots give you? Why, the ability to occasionally get Beans instead of coins. Combine this with Dream World enemies and Luiginary Ball (and maybe the gloves that give you more coins from doing that), and you won't need to care about stats in the nearest future, as well as customizing the bros exactly how you want them.
Badge effect duplication badges. Don't be fooled by its description, the Expert and Miracle Badge combo has a completely different effect than what it says. It randomly copies a currently stored badge effect and stores it for later use. If there's only one badge effect stored, then that effect is automatically copied. It also charges faster than most of the other Gold or Expert Badge combinations. Now combine that with the time freezing badges, and you'll be able to quickly stockpile this effect, making the grind to get it much, much easier.
Try the Guard/Master Badge (Protects a Brother from 6 attacks) combined with the Risk/Silver Badge (Powers up everyone on screen). That should save you some time to attack the enemy with as much force as you can without worrying about getting hurt, like for example ... Luiginary Hammer, Luiginary Wall, Zee Egg, or Star Rocket.
The Angel Bangle mixed with the Casual Bros Rank Up effect. The Angel Bangle restores 20 HP and 10 BP a turn. Casual Bros cuts the price of special attacks in half. None of the special attacks exceed 20 BP, so none of the moves with Casual Bros will exceed 10 BP. And since you heal 10 BP a turn, this means infinite Bros moves, with absolutely no restrictions outside of the Bonus Boss.
You can use Bros. Boots as a substitute for the Angel Bangle. They recharge your BP whenever you use a Jump attack, based on how much damage you do. Sounds okay at first, but what's really broken about it is that the effect stacks with Bros/Luiginary attacks that use the boots, and given that those attacks do way more damage than jump attacks do, you'll often recover more BP with the boots than you used to perform the attack in the first place (especially if you have Casual Bros on like with the above example). Enjoy never having to use regular attacks again!
Badge Charge Meter booster badges. It's possible to get this stacked up so high that you can fill the badge meter several times in one attack.
Silver + Miracle Combo. What does this do? Resets status to the last turn. But it doesn't reset how much you've beaten up the enemy, so they stay brutally mauled, you end up in a good condition again. This cures status effects and heals damage to the point you were at before, so it can act like a free combo of a Max Candy and a Refreshing Herb. For both characters. It's also very 'cheap', in that the bar for it is filled in just 14 hits (compared to more than 20 for most other powerful badges). And against Bowser Jr? It BRINGS BACK the Bros Attacks he steals! So you can go Star Rocket, Zee Egg, reset, more Star Rocket and Zee Egg! It can completely destroy the difficulty of the Battle Ring...
Boost Wear/Energy Wear. Seems useless at first, but filling your badge meter every time you get hit is a pretty damn powerful effect. Especially against the Elite Trio or Antasma, who have attacks that can hit about 10 times per turn. See how useful those badges mentioned above are? Well it's even easier when you can fill the meter every time the enemies hit YOU as well as the other way around!
The Master Gloves. If you can get an Excellent on a Bros. Attack or Luiginary Attack, your BP is refunded. With this, you can spam the most powerful moves in the game with no cost, if you're good enough. Yes, that means you can spam Luiginary Flame/Hammer, Zee Egg, and Star Rocket to your heart's content. Combine with the already broken Gold + Miracle badge combo, and just see how fast everything dies.
The Duplex Crown, your reward for completing all the Expert Challenges. Equipping it on a bro lets him have two consecutive turns in battle. With that and all the other game breakers above, you're suddenly overpowered twice over. In fact, you'd probably be a little bit too hard on the game by then. Even in hard mode. In fact, it becomes almost trivial to beat the Battle Medley in the minimum 9 turns (1 for each battle).
Goddamned Bats: Hermite Crabs. They're common, basically the only enemy in Wakeport outside of the Dream World, can't be killed with a preemptive strike and have hard to dodge, annoying attacks. You can't go four steps in some directions in Wakeport without bumping into one, and what's worse, their hard to dodge attacks? Have to be dodged ten times in a row for the 'Dodge Ten Wakeport' challenge unless you use Boo Biscuits against a single Virus in a single part of town. Oh, and they then get Hermite Crab R variants, which are also ridiculously common.
Goddamned Boss: The Elite Trio (Sergeant Guy, Corporal Paraplonk, and Private Goomp) can be rather annoying. None of them are terribly difficult to dodge or terribly difficult to defeat individually, but you can't beat them unless you take them all out in a single attack. Not in a row, on the same turn; any of them that aren't KOed will revive any that are, and they will happily combine this with a Mushroom or two to heal. Thankfully BP can be restored with badges and you can exploit Sergeant Guys cannon to damage them all at once.
Most Annoying Sound: Mario saying "Here we go!" can get extremely annoying in a Giant Battle very quickly, despite it being likely to be heard only a few times on normal occasions. It is a reminder, though, that Rhythm Mushroom/Drill Stomp can be used.
Padding: Mole Hunt in general. You have to play this mini game twice, and there's not any real story related reason for it in either instance. Seems they just wanted a way to pad out Driftwood Shore...
Save Scumming: What you might end up doing for all of the "Excellent Ten" and "Dodge Ten" Expert Challenges, as later enemies tend to have very ridiculous attack patterns. In some cases it's actually recommended to do this, as getting enemies to respawn (especially in the Dream World) tends to be a bit of a chore in the Mario & Luigi series, and getting those Expert Challenges out of the way as fast as possible ensures that your fun isn't cut short by frustration.
The Scrappy: The Dream Stone Spirit, considering how he acts like a total Jerkass to you and refuses to tell you where Bowser and Antasma were going with the MacGuffin, going so far as to turn into a giant drill machine to get rid of you for trying to get the information out of him. Needless to say, it will be immensely satisfying to beat the snot out of him as Giant Luigi. When the Zeekeeper turned the fractals of the Dream Stone into a giant coin and smashed into a coin shower, some players theorized that the Spirit ceased to exist because of this action. And nothing of value was lost.
The giant battles in general are this for some players. And there is no way to make them any easier; they are not affected by levels, stats, gear, or items, nor can you do them in Easy Mode after dying.
Stop Helping Me!: Played with during the giant wiggler boss fight. Popple (who is on your side at the time) will "help out" by annoying the wiggler, causing it to get pissed and making its attacks harder to avoid. Once you get rid of it, he immediately turns on you so he can take the treasure for himself, implying he may have been doing it on purpose.
Players think that there are too many tutorials in the game.
Surprise Difficulty: This game, is by far the hardest Mario & Luigi game yet. It has bosses with a ton of health and healing abilities, difficult to dodge attacks and some actually very hard giant bosses and sidequests. And it gets worse on Hard mode. Thought you were in for an easy ride after Bowser's Inside Story? This game can and will destroy you.
One of the key factors is that, while other games in the series were easier if the player masters timed hits, this game is basically unwinnable if you can't figure them out.
That One Attack: Earthwake's hammer attack for starters, since it's very easy to fail to block, does a ton of damage... and so far, seemingly not one person on Youtube has managed to completely avoid it. Oh, and he swings about 10-15 times in a row on hard mode... Hint: Swing when you hear a chime.
Other notable examples include Antasma's bat attack in his final battle (it's not so bad, but it's the potential secondary effect that makes it this: Antasma pulls Mario into a Dream Within a Dream and begins to chase him down while spitting dark flames, and Mario has to find the correct exit to wake up, the others contain spikes that can combo you AND won't pull you out of the dream), Pi'illodium's hammer transformation attack (hmm, every boss that becomes a hammer tends to become That One Boss), Bowser's chase attack in his first battle and a few others. Pi'illodium also has another one in the form of his self destruct move, which operates on a real-time timer in a turn-based game.
The Zeekeeper's dimensional rift attack. Even when the gyro controls are actually working properly, it's still a pain to avoid the energy balls AND his ramming attack.
In the Battle Ring, the attacks of the X version of Antasma all become That One Attack, because every single one has the chance to make you sleep. It's almost a relief that the boss who follows after is one of the most fun bosses to fight.
The Beehoss' bee swarm counterattack. When attacked, it fires a hard-to-dodge swarm of bees. Jump on the bees instead of jumping over them? They counter your counter with an unavoidable counterattack. This mechanic applies to their standard attacks, which are no easier to dodge.
The Mechakoopas' fireball march. In theory it sounds simple: bait them by moving into their path, then move back once they're done shooting. In practice, it's all but undodgeable, as there's no way to move out of their way and back quickly enough without getting hit by another Mechakoopa's fireballs. No, you can't just jump over the fireballs, as they constantly fire if you're in their path. There's a good chance they'll use this attack before you can even move, up to five times in a row.
A way to dodge is to wait at one end of the battlefield until you see the exclamation mark indicating that the Mechakoopa saw Mario, then move to the other end of the battlefield and hop over the 1 or 2 fireballs the last Mechakoopa shoots at Mario, before jumping over the Mechakoopa itself.
Mammoshka's giant rock. It hits both Bros for massive damage and you have to hit it 3-5 times to get rid of it. Both Bros have to hit it at the exact same time; if one is slightly off, then the rock will crash into the other Bro for massive damage. That alone would be challenging, but the worst part is that it goes off-screen the 4th or 5th time it is hit. Unlike Pi'illodium's hammer, which comes down on a timer, there is no tell for when it's coming back down aside from memorizing the timing.
The Zeekeeper. Due to how giant boss fights work in the game and since this boss is constantly fleeing from you, said act of fleeing and its attempts to shake you off are technically his turns, meaning you have to wait a while before getting to do anything of your own accord.
It only gets worse when it begins to travel dimensions, instructing you to move with the gyro controls. Due to a fairly common Game-Breaking Bug, the gyro controls can often fail to register, making this fight impossible to win unless by sheer luck you can dodge it's attacks by not being targeted.
Earthwake. Giant hammer formation attack causes hell if not countered properly. And it comes right out of nowhere after a simple fetch quest too...
Giant Bowser, because he's by far the most complex giant boss in the game and introduces a ton of new mechanics you need to learn/attacks you need to dodge or counter. It's gyro phase is arguably even harder due to a common Game-Breaking Bug mentioned above.
The second and final fight with Antasma. Not only are all of his attacks hard to dodge, but they also have a chance of putting Mario to sleep, forcing you to avoid Antasma's fireballs and going into one of five holes to find the exit.
Dreamy Bowser, which continues the trend for HARD final bosses of the Mario & Luigi series. For starters, you can do no damage to his actual body until you can defeat his right arm, and if you don't defeat his left arm, he'll grab the brother to prevent you from using bros attacks and then fling them away to deal potentially massive damage to them. Second, his hammer attack is EXTREMELY difficult to avoid given the fact that he targets both brothers. Third, he can summon Dream World enemies, and, while those enemies fight you, he beings to dine on meat that can recover his health, to both himself AND his arms. Finally, he can summon a background enemy to shoot cannonballs at you.
Big Massif in the Dream World. If you are to kill any of his Mooks, depending on how many you killed, Big Massif gets a Power Bonus; since all of your Dream World attacks are Herd Hitting Attacks, this is almost guaranteed to happen. Worse yet, he summons more and more of them every turn. You can't just relegate yourself to weak attacks to avoid killing them either, as Big Massif has a chasing attack that grows in strength for every Mook he has with him, which is further boosted when he's pissed off. You have to keep the Mook count to a minimum and - more importantly - get good at dodging Big Massif's attacks, or he'll mop the floor with you.
Speaking of Big Massif, there's also his disciples. All four of them have a special gimmick in their fights that turn each of them into a Beef Gate (especially BeefCloud) and require you to have a working knowledge of all your battle skills up to that point. If you don't, then they could be even more frustrating than Big Massif himself.
The hardest of the disciples is Thunder Sass. He has the lowest count of HP for all four disciples, but this is well made up for by the brutal gimmick added to the fight: you can only counter-attack him. Yes, the Jump and Hammer Attacks are banned in this battle, as well as your Luiginary Attacks. Oh, and badge effects are banned too. This means that healing is the only thing you can do when you get your turn. So if you can't counter-attack, this battle is psychically IMPOSSIBLE to win. Combine this with hard-hitting difficult-to-dodge attacks, and you've got a recipe for one of the more difficult bosses of the game.
Pi'illodium. That hammer attack and the missile attack it uses are killers, and its self destruct timer is even worse (though it IS possible to defeat it without triggering its self-destruct timer).
That One Level: Dreamy Somnom Woods can easily be this. The maze? Check. Lots of puzzles and confusing rooms? Check. That One Boss? Well, the Zeekeeper is fought at the end (with easily broken motion controls!) and Pi'illodium is fought at the beginning (with hammer attack and self destruct timer), so you end up having one annoying boss before you enter and one annoying one fought to leave. Oh, and you'd better not mess up the Zeekeeper fight on Hard mode, unless you want to see a lengthy cut scene about ten times.
That One Sidequest: The Mad Skillathon Challenges. Battle Broque Madame. The Battle Ring in general. The Giant Battle Ring even compared to the last three. And then the Hard Mode Battle Ring which is pretty much the meanest, most difficult part of the entire game due to extremely stingy turn limits and long, difficult battles with hard to dodge attacks.
Some people are already giving this game flak for having Bowser be the final boss. Though as mentioned above, the move is being received much more positively than in Paper Mario: Sticker Star, due to Bowser breaking out of his Dumb MuscleBig Bad Wannabe niche usually seen in the Mario RPG's while still keeping his personality.
Viewer Gender Confusion: Antasma was commonly mistaken for a female when previews for the game first came out, thanks in large part to his gender-ambiguous clothing and his resemblance to Cackletta, a previous female villain whose gender was more easily discernible.