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.
Author's Saving Throw: Mario Kart Wii got released in Europe first. This is most likely in order to make up for Nintendo's earlier announcement they would release Super Smash Bros. Brawl in June 27, 2008, that is, three and a half months after North America's March 9, 2008.
Mario Kart DS has Waluigi Pinball, which is Exactly What It Says on the Tin: a giant pinball machine where players are launched to the top, then race back down while avoiding bumpers and giant pinballs. It even replaces the usual item jingle with a more casino-y one.
Mario Kart Wii has Koopa Cape, which features a large river that speeds up players that drive in it, and a shark tunnel. Mario Kart 7 takes it one step further by filling the shark tunnel with water to complement its underwater driving mechanic.
Mario Kart 7 introduces courses that forgo the usual roundabout design, instead using checkpoints rather than one finish line. Most people regard these as the best tracks in the game, especially Rainbow Road.
Breather Level: Mario Kart 64's Rainbow Road, unlike the tracks before it and its Super Mario Kart counterpart, is merely extremely long, and, unlike later incarnations, has rails on the entire track instead of just the curves.
Broken Base: Maka Wuhu had one for the online players due to the infamous cliff-falling glitch that puts the user of it ahead of others by several seconds. One portion considered it unfair for those who don't know about it or just want a simple race while the other portion said it's fair game for anyone since it's in there. Nintendo's response to the outcry by keeping said glitch did not help ease the fire, so to speak. In May 2012, they released a patch that would fix the exploit. After the patch's release, it became mandatory to have installed to be able to play online.
Character Tiers: In every single game, but most notably in the 3-D games. Mario Kart Wii had each character give invisible bonuses, with the more favorable quickly reaching Tier-Induced Scrappy levels. 7 seems to have averted this with the customization system and lack of significant character bonuses.
Almost a standard in the Wii version, where most people will only use a bike and certain characters just for the sake of being slightly faster than others.
In Mario Kart 7, Metal Mario became the go-to character for competitive players because heavyweights were considered to have an advantage, and Metal Mario takes up the least amount of screen space. Between that and Japanese players' love for Metal Mario, he became the most-used character in Mario Kart 7 by far.
Toad is by far the fastest character in 64 and Super Circuit.
"Snaking" is a technique where you constantly powerslide back and forth to gain mini-turbos on straightaways (normally you're only supposed to get mini-turbos when making a sharp turn). It's been essential for setting world records since at least Mario Kart Double Dash, but was rendered almost impossible from Wii onwards by making the mini-turbo dependant on how hard you turn during your powerslide.
Bikes in Wii, they massively overshadowed karts. More so with characters like Baby Luigi, Funky Kong or Daisy. Especially Funky Kong.
The series have tracks that can cut down on your laps greatly due to abusing exploits of the checkpoint system (this determines where Lakitu drops you off if you fall from the track). A notable one is the glitch in the Grumble Volcano track in Mario Kart Wii; if done correctly, the player can finish the race in 30 seconds or less. Naturally, nearly everyone abused the exploit online and it was more obvious when people started to spam vote for the track. Mario Kart 7 also has a similar one with the Maka Wuhu track that allows people to skip huge sections of the track. Not only people began to abuse this online as always, but the exploit was found almost days after the game was released.
Several items are game breakers depending on the game they are used in:
Super Mario Kart had the mushroom give a huge boost and the star gave players insane speed boosts for several seconds which allowed them to cut across tracks with dirt/water/sand, etc. These items were nerfed and adjusted to be less game breaking but still useful, but perhaps the biggest game-breaker was the feather, which allowed you to jump over the boundaries of the track, allowing for massive shortcuts. That item was never featured in another Mario Kart game after that.
The multi-banana peel in Mario Kart 64 gave you a trail of 5 peels, which meant up to 5 protections from shell attacks and also 5 peels to spray the tracks with. Later games reduced the item to 3 peels.
Mario Kart Super Circuit gave red shells a secondary function by allowing players to drop it behind them and the next player that passes it gets attacked by it. This made it too easy to place it by gaps or jumps in order to make people fall off the track, so the function got removed in future games.
Nearly every special item in Mario Kart Double Dash!! is a game breaker; Mario and Luigi's fireballs are a spreadshot that can hit multiple people, Bowser and Bowser Jr.'s giant shell is basically a faster and bigger version of the green shell that's difficult to avoid, Donkey Kong and Diddy Kong's giant banana peel is also difficult to avoid and it splits into 3 smaller peels when struck, Yoshi and Birdo's egg attack released several items when it broke and one of them could be a star, and Peach and Daisy's hearts allows you to absorb up to two items, including most special items, for your own use later, Baby Mario and Baby Luigi have the Chain Chomp which not only boosts their speed while it's out, it also wrecks any obstacle on its path (including other racers), Koopa and Paratroopa got exclusive control over the Triple Red/Green Shells, Toad and Toadette could spam the Golden Mushroom anywhere and jump to the front of the pack, and Wario and Waluigi could blow anyone off the road with the Bob-omb. And then there are Petey Piranha and King Boo who can useallof the special items available in the game...
The Boo item turned the player invisible, which made them immune to all forms of attack, and it stole another player's item. Players could also drive off road in the DS version without loss of speed with the Boo item as well.
Maple Treeway in Mario Kart Wii and 7 have piles of leafs that often contain items. One of the items you can get is the Starman. And you can pick this up in any place you're in.
Double-shielding with items (holding one item in the reserve, and another behind you to protect from attacks). Removed from 8.
The Egg 1 kart is a bottle rocket. It boasts extremely fast acceleration, very finessed steering, and good handling in general. Egg 1 became an excellent vehicle for posting superb time trial records in DS because its ultimate weapon was snaking abuse. A bit watered down in 7, where you can customize the wheels to adjust its stats (Roller wheels replicate its acceleration perks) and snaking has been jolted from gameplay. The only downside is that it gets flung far away if a heavier vehicle strikes it.
Goddamned Bats: Some levels have hazards which can pop out at bad times to slow you down, including sliding walls, falling presses, and, yes, bats. Sometimes, the goddamned bats can be the other racers themselves as they can get in your way when you are trying to pass them or crash into them while performing a power slide and losing your momentum. This is much more noticeable with the AI since they don't deviate from their preferred path too much.
Hell Is That Noise: You will panic every time you hear the alert of a homing item. Especially the Spiny Shell.
In Mario Kart Wii, characters scream things like "YEAH!" or "WOOHOOOOOO!" at the top of their lungs for almost everything they do, even for little things like mini-turbos and wheelies. Although certain characters get more attention for it than others, when it comes down to it, every character could be considered equally annoying due to the cartoony ear-piercing voices.
When playing with a Mii in 7, get ready for "YEP YO! YEP YO! YO! YEP YEP! YEP YO!"
Funky Kong in Wii is very loud, very hammy, and is without question one of the most popular characters to use in competitive play. Every third race online had a bad tendency to be punctuated by a chorus of "GOGOGOGOGOGOGOGO! WOOOO! WOOHOO!"
Toad from Mario Kart 64. "HERE WE GO! I'M THE BEST!AHHHHHHHH!"
Honey Queen. BZZZZZZ BZZZZZZZZZZZZZZZZZZ!
Crashing into penguins, plants, moles, etc in that game played this horrible squealing noise.
The "incoming shell" beeping alert. Especially when it's a blue shell and you can't do anything about it.
The beeping sound when you've got shells spinning around your kart in 7, especially if you've played the Metroid series, you can mistake it for the Critical Annoyance alerts when Samus is low on energy.
Daisy, who is mentioned as a possible scrappy across the franchise, is in some of the later games (her classic "Hi, I'm Daisy!" line comes from Double Dash).
Honey Queen in 7, as she is an extremely minor character who had just appeared in a small handful of missions in SMG and SMG2 before and is widely considered as being undeserving of a spot in the roster, getting in over beloved veterans such as Waluigi or Dry Bones. Her horrendous voice acting doesn't help matters, either.
Metal Mario is even considered a Scrappy to some people, because he is only a Metal version of Mario with slightly heavier stats. Some people even hate his voice. That being said, Japanese players love him.
Any baby character except Baby Mario and maybe Baby Luigi has gotten shades of this, due to all of them being similar to one another and are found as wasting too many slots.
The Spiny Shell, if the examples floating around didn't make it clear enough. Sure it's annoying when you're in first and then you get hit by the Spiny Shell allowing every other racer a chance to pass or catch up to you, but it also doubles as a Power Up Let Down for the Spiny Shell user. Even if the user can stop the 1st place guy, they still have several other racers ahead to contend with. Thankfully the Spiny Shell received a nerf in the DS and 3DS installments, since you can see items racers collect in both installments and act accordingly, but also the shell was stripped of its wings from Mario Kart 7 onward.
The Thunder Cloud from Wii is even more reviled. The idea is that you get a big increase to your speed as long as you have the cloud above you, but it zaps you after a few seconds. The result is that the player has to choose whether to pass it on to an opponent and lose the speed buff, or keep it and risk getting shrunken. All in all, not too bad, yet for some reason the game designers made it so that it triggers as soon as you get the powerup, regardless of where you are on the track. The final nail that makes it such a hated item is that it can be picked up in any position, even in last place. Needless to say, many fans are glad that it hasn't reappeared in any other game.
Coins in Super Mario Kart and Mario Kart: Super Circuit. You need to hold coins to increase your speed (the boost caps at 10 coins) and getting hit by items, crashing into course hazards, or falling off the track made you lose coins. Even bumping into another racer made you lose a coin! The games also made the coins an item to give you 2 coins instantly, but it could also screw you over if someone behind you has a red shell or the like. Mario Kart 7 changes the coins mechanic slightly where not having a lot of coins won't totally screw you over and bumping into people won't make you lose coins, but you can't hold more than 10 coins and you will lose 3 coins (or two if your coin count is low) every time you get attacked or fall off the track, which makes holding onto your coins a pain in the ass. Luckily, coins regenerate. Unluckily, you need to collect coins to unlock parts for your kart and you will be playing for a long time since you will need to collect several thousand coins and even beyond 10,000 coins just to get everything. This is made worse due to only being able to hold up to 10 coins per race.
The Super Leaf in Mario Kart 7. Very useful for blocking red and green shells, but did not provide any use whatsoever to players who had nothing to hit or were stuck in a position where they needed a ranged item or obstacle item.
The very system of dropping held items since Double Dash!! when hit by certain items from opposing racers. It's particularly painful when you are hit by a Spiny Shell and lose everything you were using or saving.
Toad's Turnpike. Extra Cup. Now, Extra Cup normally just mirrors the tracks. For this track, the course is mirrored...and the traffic cars are oncoming. Welcome to Hell.
Rainbow Road ends up being this for a majority of every game except its really long and safe version in MK64 (which averted the difficulty after the first Mario Kart), thanks to the general lack of railings and the abundance of sharp turns and narrow pathways. That's disregarding everyone trying to throw explosive flying shells at you.
Mushroom Gorge in the Wii version. At least 1/4th of the track is over an abyss with only bouncy mushrooms to launch yourself across to another mushroom until you hit the other side. Hitting the mushrooms at a wrong angle will most likely throw you into the pit. Using a Bullet Bill while over the mushroom pit can also be disastrous if the power up runs out when you're over the pit instead of a mushroom or the ground. Even simply going too fast with a mushroom item or a star can throw you into the abyss. To make matters worse, you also have to hope people don't try to target you with a red shell, spiny shell, or a thunderbolt as you cross the gap. And to even think it's just the third track in the game...
Baby Park In Double Dash is also just the third track in the game, is named after the baby Mario Bros, is just an oval with two turns, has no hazards, and is so small that racers must do seven laps instead of three. So what makes it so hard? Basically, the track is so small and item boxes so plentiful that what would be a simple back-and-forth battle in other tracks becomes a chaotic maelstrom in Baby Park's tight spaces. It's also not very hard to drop behind most of the racers, grab a powerful Special Item, then launch it and blast to first in a matter of seconds, only for that to happen to you because of all the people you knocked behind you. And so on and so forth...
Maka Wuhu was one in 7's online mode, due to an infamous glitch which was easily abused. This has been fixed, as of May 2012.
Many people initially mistook Toad for a female in Mario Kart 64 because of his localized voice (it was more masculine in the Japanese version), which is the reason for the more raspy voice Toad continues to have to this day. Ironically, Toad has been voiced predominantly by female voice actors since then, while the 64 voice actor was male.