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.
Also Mario (and Luigi) himself: Mario is a ruthless One-Man Army killing anything in his path, not caring if his foes WANT to hurt him or not, captures countless lands, and basically waged a war against a rivaling kingdom with many casualties on their side, just to rescue a princess.
Although even the enemies who don't pursue Mario if he jumps over them (instead of on them) would still hurt him if they touched him, so it's not clear whether they don't want to hurt him or they do but they're incompetent.
And also, kidnapping another country's regent wouldn't signify an act of war?
As an addendum to the above, some argue that Mario is genuinely good, but a Heroic Comedic Sociopath. He genuinely wants to save Peach, but he has too much fun basically slaughtering the equivalent to entire armies (there's some actual canonical basis for this, notice how Mario tends to sound like he's having fun in some of his ingame sound bytes?).
Peach and Bowser have the 'kidnapping' thing going on to make money, since only Mario and Luigi can get coins out of those blocks.
Or Bowser's feelings toward Peach are actually mutual.
Cracked had a lot of fun with the interpretation that Bowser is actually in love with Peach but bad at expressing it; Peach has conflicting feelings and notably never denies being the mother of Bowser Jr. when Bowser Jr. claims she is. Bowser is also a Well-Intentioned Extremist, who captures the Yoshis because they're an ecological menace (they eat anything), until he finds time to find a permanent solution to the crisis, due to the fact that he captures them, rather than killing them. He may also be the also the only person capable of ruling the land, as he has time to build, maintain and run seven castles simultaneously, manages to conquer and subdivide the lands into more effective zones, and find time to kidnap Peach. He essentally keeps trying to perform a Benevolent Alien Invasion but it keeps getting screwed up by Mario...by the way, where was he while Bowser was doing this anyway?
Another Cracked article assumed that Peach has a case of Stockholm syndrome, since she says Bowser kidnaps her, never hurting her, and and playing sports with her.
A How It Should Have Ended video portrays Bowser as attempting to make peace treaties with Princess Peach due to Mario always killing his people.
Base Breaker: Waluigi to a pretty big degree. Those who hate him say he is a ridiculous character with no reason or purpose to exist. Those who like him say that he is an unique character that can fulfill many roles. And it goes on and on.
Bizarro Episode: The US Super Mario Bros. 2 (known as Super Mario USA in Japan) is pretty much this, as it has nothing to do with the rest of the main platformer series, and is revealed to be All Just a Dream in the end. This was because it wasn't the actual sequel to the original Super Mario Bros. The Japanese version of Super Mario Bros 2. (called Super Mario Bros.: The Lost Levels in the US) was the real sequel, directly following the previous game, while the US version was actually an entirely different game called Doki Doki Panic, only with four Mario characters added in place of DDP's characters. This was done because SMB:TLL was deemed too difficult and too similar to the original game. US players had to wait until Super Mario All-Stars, a collection of remakes for the NES, came out to play The Lost Levels. So the Mario platformer series has TWO second installments, though SMB2: TLL is the actual canon sequel while SMB2: USA is a BLAM episode. YMMV on which you prefer though.
Crazy Awesome: The series (and most characters) as a whole. Especially Wario, Waluigi and Bowser
Demonic Spiders: The series has two main ones: Hammer Bros., and Lakitu. Hammer Bros. because they lob a barrage of hammers at you, which is jarring since you mostly jump over most hazards. Lakitu because they mostly float out of your reach and they throw the already hard-to-kill Spinies at you.
Despite only appearing in one game and its ports/remakes, Wart is one of the franchise's most popular villains. Being one of the few non-Bowser Big Bads in the main platformers probably helps set him apart.
The Koopalings. They are quite the colorful bunch, having different personalities and different hairstyles. No wonder fans were upset when Bowser Jr. replaced them.
Iggy in particular stands out; the New Super Mario Bros series remade him as a Laughing Mad, Ax-Crazy boss that's capable of walking on ceilings (no, not clinging, flat out walking).
Also Ludwig. Being the "boss" of the group and is portrayed as the most capable of them.
Rosalina has become popular for being a princess that you don't have to rescue. Not many people were happy when Lubba replaced her in Galaxy 2and she only appears in the end. On the other side of things, fans were very happy when Super Mario 3D World included her as a fully playable character.
Waluigi also fits, partly due to the fanon filling the gaps Nintendo leaves open . People actually lamented his absence from Mario Kart 7. And when Mario Kart 8´s trailer was released, he was one of the first characters to be shown.
Although Waluigi still has plenty of haters, so this would make him more of a base breaker.
Ever since Mario & Luigi: Dream Team, there have been two more sets of characters who've ended up becoming this, the Big Bad Antasma and the somewhat beef and muscle obsessed Massif Bros. Will either be Fawful's replacement as fan favourite? Hard to tell yet, but it's possible.
Evil Is Cool/Love to Hate: Bowser is one of the most beloved and classic video game villains of all time. He's also one of the few Mario characters that has a fleshed-out personality. Even though he suffers Villain Decay intermittently, he is able to make up for it by reversing it in games like Super Mario Galaxy.
Fandom Berserk Button: The game is called Super Mario Brothers, NOT Super Mary-Oh Brothers, as some old Mario commercials would lead you to believe.
Asking for Super Mario Bros. 4 to be made will lead irked fans to pointing out that it already exists — only it was called Super Mario World in the US.
Mario and Luigi's last names are not Mario — as far as Nintendo themselves are concerned, they have no last names.
The Gold and Blue Toads in New Super Mario Bros. Wii have been given the names Wolley and Yvan, respectively (pronounced "Wally" and "Ivan").
Fridge Logic: The manual for Super Mario Bros. 1 stated that Bowser used his dark magic to turn the people of the Mushroom Kingdom into trees and bricks, and Mario spent the entire game destroying the latter. So when you think about it, Mario is actually a mass murderer.
It's never said that Mario hitting the bricks destroyed them (other than what the 8-bit pixels seemed to represent); if anything, once the bricks were broken, the people were probably returned to normal (that's the way it goes in these types of games anyway). Besides, this was never mentioned anywhere outside of the instruction manual for that one game, which is suspect as the blocks show up in almost every Mario game afterwards.
Or, the fact that it's specifically mentioned that the people were turned into bricks and not blocks could be significant. Hitting and breaking the blocks just detaches the individual bricks from each other without necessarily destroying them.
Another example of fridge logic: how do the many enemies that walk in a straight line and never change direction until they bump into something (such as the Koopas described under "Fridge Horror" below) get between the two objects they're walking back and forth between in the first place if they can't walk or jump over them? Does Bowser really go to all the trouble of finding countless pairs of immovable objects and putting minions between them before kidnapping Peach? How do the authorities not start to notice this pattern and take precautions to protect Peach whenever Bowser starts dropping minions between immovable objects?
Probably the most overlooked example of this trope is the fact that the Super Mushroom would technically kill Mario if not for its beneficial result. Some brightly colored mushrooms can be poisonous.
What about what happens to the coins you have that you collected when the brick blocks turn into coins when you hit the P Switch? If it turns all coins into bricks and all bricks into coins, what happens to the coins you carry?
Good Bad Bugs: The "small fiery Mario" glitch. If you hit Bowser and the axe at the same time at the end of an x-4 level, you'll start the next level as a large Mario who dies in one hit. Take a mushroom and you become small; take a Fire Flower and you become small and fiery.
Also, a related glitch: if you're small and you hit Bowser and the axe at the same time, Mario dies but the level still registers as a win, leaving Toad saying his "Thank You Mario/Luigi!" line to a blank screen.
There's also the fact that the correct pipes in the World 8-4 Pipe Maze will have the Pirahna Plants inhabiting them suddenly disappear as you approach them. This significantly reduces the potential aggravation of guessing the correct pipe.
If you jump on the axe just as the timer reaches zero in any castle level, you'll get a huge bonus of 50,000 points. This is because of a bug in which the timer rolls over to 999 and keeps counting down from there. However, this does not work in the NES version, since it doesn't give you a time bonus for castles. This can only be done in the "Vs." (arcade) and Super Mario All-Stars versionsnote not to mention most, if not all versions of the Japanese Super Mario Bros. 2.
Incest Yay Shipping: Toad and Toadette, though it seems that it's because people don't know that the two are brother and sister. It doesn't help that Nintend can't make up their minds about whether they're siblings, friends, dating, or what.
LGBT Fanbase: Bowser is incredibly popular with the gay fandom, most notably with furries.
Never Live It Down: "Hi, I'm Daisy!" It doesn't help that while a lot of Mario fans don't play the spinoff games all that much, they do play Mario Kart games, and for many Mario Kart: Double Dash was their first impression of Daisy.
Daisy for some. Aside from the fact she technically only uses the line in a few games, her "Hi, I'm Daisy!" quote has become something of an online meme for her character. This is also regardless of the fact that Mario characters are all known for shouting annoying one-liners, so it's likely a case of bandwagon.
Her Baby counterpart takes it Up to Eleven in annoyance. If only because there has never been a Baby version of her, and just putting her again in the game makes it worse. Being there for a simple counterpart to Baby Peach doesn't help matters either.
Pretty much all the Baby characters could count at some point due to their crying.
Villain Decay: Bowser tends to go back and forth with this to a nearly unprecedented degree; though he's usually a genuine threat in the 'core' games (ranging from downright silly plots to accidentally destroying reality after nearly conquering it). In spinoffs, though, he's typically little more than a comic-relief nuisance, a reluctant ally, or even a near Woobie level Butt Monkey as in Mario & Luigi Superstar Saga.
"Somewhere My Love", the song Mario and Luigi trick the Goombas into dancing to... La, la, LA LA....
"Walk the Dinosaur".
Foe Yay: It's possible to see some between Lena and Daisy.
Funny Moments: Mario and Luigi are chained as they get their picture taken, when they mistake the cameras for guns.
Mario: Are we dead?
In addition, the dancing Goombas can also be seen as one of the few intentionally funny moments.
Ham and Cheese: Dennis Hopper's acting is okay in some scenes, but in others, he's clearly having fun overacting and taking his role not at all seriously.
Harsher in Hindsight: The two towers that dominate Koopa's Manhattan-inspired city, one of which looks half-destroyed (actually, it's not finished construction yet, but the visual effect is the same), and the other of which has a glowing stylized "K" on the side that looks like, depending on how you see it, either an explosion or a gaping hole.
Even worse in the climax when the dimensions begin to merge, including a shot which can visually can be described as the World Trade Center disintegrating.
Special Effect Failure: Amongst all the revolutionary visuals and complicated animatronics for Yoshi and the Goombas, the devolved King Koopa puppet looks like an escapee from a bad episode of The Muppet Show.
Squick: The fungus, in-universe. Mario in particular is constantly grossed out by it.
Vindicated by History: It seems that audiences are warming up to this movie. Probably because looking back, it still kept the basic plot of a Mario game, but with a few changes, or simply for the So Bad, It's Good factor.
Visual Effects of Awesome: Much like Jurassic Park, this film had to literally invent new technology to make much of its visual effects look as realistic as they do. Unfortunately, Jurassic Park's effects were a much more explicit focus, so it gets more attention for its influence on the industry.
Daisy appearing in the sand.
Yoshi. For an animatronic puppet, it looks like it just stepped out of a time portal to the Jurassic Era.