List of Mario Kart 8 pre-release and unused content
This is a list of pre-release and unused content for the game Mario Kart 8.
One of the ideas suggested early in development was having a drill that attached to the players' karts to allow them to tunnel through the ground, but the idea was scrapped since the team did not think it was interesting enough.
Twisted Mansion was originally called Boo House. Kart noises in the E3 build are recycled from Mario Kart Wii while in the final version they are replaced by new engine noises. The course intro music in the E3 build was from Mario Kart 7, while the results and menu music was from Mario Kart Wii, much like the E3 2011 demo for Mario Kart 7. Character voices are recycled from previous games in the E3 build and newer builds provide newer voices. Players are unable to slipstream in the E3 demo. Characters did not hold items in their hands in the E3 demo. Donkey Kong's Standard Bike color was brown, but is yellow in the final version. The Galaxy Air advertisement in Toad Harbor at the starting line was replaced by a Flower Cup logo and the cloth used a different texture while music had a different banjo. In early builds, the buttons "a" and "b" were replaced by upper case versions. Thwomp Ruins in the E3 trailer lacked flowers, the start/finish line where it was in the final version, the anti-gravity section before it was a normal section and the section with four torches was replaced with a trick section (ramps). The Goomba Towers found in Mario Circuit were both taller and harder to avoid unlike the final build of the game. In the trailer from E3 2013, multiple Piranha Plants can be seen at the same time. The artwork of the items in the roulette were recycled from Mario Kart 7 and Mario Kart Wii unlike the new upgraded ones in the final build. There were also no Pokeys in GCN Dry Dry Desert.
Triple Bananas originally were in a line of three and obtainable in 1st place like in Mario Kart Wii and Mario Kart 7 instead of circling around the kart and obtainable in either 2nd to 4th place. The same applies to Triple Mushrooms in that they also didn't circle the kart. If the players played as a character with facial hair in the E3 demo, their mustaches would not blow in the wind, unlike the final game. Players were also able to grab a second item while dragging one behind the kart in the demo, which cannot be done in the final game. The sound the item roulette makes is different in the E3 demo whenever it's going through the items. The sound when the player collects a coin is also different in the demo and also the gravity sound when a player goes through the anti-gravity pad to switch to anti-gravity mode is different.
In the E3 demo, some (if not, most) of the items were missing or either unobtainable due to it being only a demo and added to the final game, some notable examples of the missing/unobtainable items were the Bullet Bill, the Spiny Shell, the Super Star, and Lightning. The HUD also looked different in the demo, having solid numbers instead of the digital ones in the final game; the same also applies to the countdown timer. The kart customization was also absent from the demo; players would instead choose a character and race with a kart or bike pre-made for that character. Also, the players make two laps per race instead of three (seven in Baby Park): this was probably done in the demo because the CPU still wasn't finished.
The vast majority of the courses shown before release were left mostly unchanged between their initial unveiling and the final version, and most of the differences are only subtle details that generally do not affect the gameplay, one example of these changes can be seen with the design of the Toad Toy Store, in the E3 build the windows were much larger and had a checkerboard design in their layout, in the final build they are much smaller and aligned in rows, and the wall surrounding them is painted green rather than pink or cyan like the rest of the building.
Lots of music was changed between the trailers and final release. This is likely because the music had not yet been orchestrated at the point in time when the trailers were released. All of the music in the E3 build had slightly different instrumentation, and the trailers released at the time, in December 2013 and February 2014, are all different from the final game in a similar manner, though the changes are more subtle when comparing the final game to the more recent trailers. The earlier music used for Mario Circuit can be heard in the E3 trailer. 
Originally, the minimaps on the were very similar to Mario Kart 7 ones; dark checkered gray background with a white colored course. In the final release, the minimaps have a checkered white background with a light blue colored course (rainbow colored for all three Rainbow Road courses that appear in this game). Incidentally, white colored maps would be used for all tracks (including the Rainbow Roads) in Mario Kart 8 Deluxe.
December 2013 trailer
The start/finish line for Thwomp Ruins was originally at the first tunnel entrance.
The second downloadable content pack was originally named "Animal Crossing: New Leaf × Mario Kart 8" before being changed to the more general Animal Crossing × Mario Kart 8; this was also reflected in the Animal Crossing course, which featured the Animal Crossing: New Leaf logo in the original screenshot before being changed to the more general Animal Crossing series logo. The Able Sisters store appears on the released track, but in the original version the sisters themselves are not outside. In addition, the store is not barred off.
Track-wise, what seems to be Shy Guy Bazaar was originally supposed to appear as a DLC track, but was replaced with either Ribbon Road, Cheese Land or Neo Bowser City, as shown by its code name in the files.
Wild Woods lacked the Item Boxes at the beginning of the course that are present in its final build.
Among the layout images of the game an unused speedometer was found, its layout indicates that it was meant to be a digital and analog speedometer at once, with a decimal separator in the digital part. Another layout file in the same archive, cm_L_LoadIcon_00, is apparently meant to show said speedometer, as its elements named P_LoadIconMeterL_00 and P_LoadIconMeterR_00 match the size of the speedometer, while P_LoadIconMeterNum_00, P_LoadIconMeterNum_01 and P_LoadIconMeterNum_02 match the size of the digits, further confirming that it should display three digits as the layout image shows, however its name might indicate that it was intended as a loading screen indicator to show how much of the game was loaded. Mario Kart Tour effectively uses an animated analog speedometer to indicate that the game is loading data.
Five unused racetracks have been found within the game:
Pink and green colored Toads can be found in the game's files. These were meant to be seen with the others in Rainbow Road. Various unused objects can be also found, which include a tree and a fruit basket that is not referenced anywhere.
Four unused cup icons have also be found within the game, which show a Yoshi Egg, Shine Sprite, Boo, and Spiny Shell. These icons use the same borders as the in-game icons, but sit in a plain background without any decorations. An updated version of the Yoshi Egg icon is used for The Legend of Zelda × Mario Kart 8 Add-on Pack as the logo for the Egg Cup. These unused cup icons possibly imply that DLC would be more oriented towards the Mario series, and not crossover with other series.
Unused body part icons have been found. A prototype Pipe Frame body is seen with two exhaust pipes rather than one in the final build, more similar to the Mario Kart 64 build of Pipe Frames. A prototype vehicle which looks similar to an early build of the Prancer is seen. Icons of the Standard Kart and gliders, plus the Egg 1 from Mario Kart 7 are found, most likely place-holder icons.
An emblem for Kamek can be found, hinting he had been possibly planned for inclusion as a playable character.