"Link Kart 8" or "Morton Kart 8", for how popular those characters are among players (the latter due to the double-whammy of being a heavyweight, statistically the best choice for a high top speed, and a Koopaling; and the former simply because of the Zelda series's popularity).
In Spain the game is popularly called "Kartocho", a portmanteau of "Kart" and "ocho" ("eight" in Spanish).
Killer App: Considering how well the original game sold — approximately two-thirds of all Wii U owners purchased it — it very likely prevented the system from going down as one of the biggest failures in videogaming history instead of "only" being Nintendo's lowest-selling home console. Weirdly enough, Mario Kart 8 Deluxe also ended up being this for the Nintendo Switch to some extent; while not the killer app for the system (that was The Legend of Zelda: Breath of the Wild), it was still held up as one of the biggest reasons to purchase a Switch, and ended up outselling the original version in just under a year. By the end of 2018, it had dethroned Super Mario Odyssey as the top-selling Switch title. Between the two installments, Mario Kart 8 has become the highest-selling game in the entire franchise.
Limited Special Collector's Ultimate Edition: A deluxe package which came with a figurine of the infamous Spiny Shell. It was a Nintendo Store exclusive in North America but was more widely available in the rest of the English-speaking world, who also got some other little trinkets depending on where the package was ordered from such as key rings or a Bullet Bill shirt.
Meme Acknowledgement: In 2019, the Nintendo Switch got a news bulletin for games starring Luigi to celebrate the upcoming release of Luigi's Mansion 3. The message for Mario Kart 8 Deluxe notes that "it's not polite to stare at rivals as you pass them", referencing the infamous Luigi's Death Stare.
The Other Darrin: An interesting variant. While Takashi Ohara is the voice of Skyward Sword Link, he also replaces Kengo Takanashi as the voice actor of Breath of the Wild Link due to using the same voice clips as Green Tunic Link.
Prop Recycling: Some of the battle arenas in Deluxe reuse assists from race courses. For example, Wuhu Town uses the same background from Toad Harbor.
Returning from previous Mario games are Charles Martinet as Mario, Luigi, Baby Mario, Baby Luigi, Wario and Waluigi, Samantha Kelly as Peach, Toad, Toadette and Baby Peach, Kenny James as Bowser, Kazumi Totaka as Yoshi, Caety Sagoian as Bowser Jr, Deanna Mustard as Daisy, and Laura Faye Smith as Rosalina.
This game was the last time Takashi Ohara reprised his role as Link from The Legend of Zelda: Skyward Sword.
Yuki Tsujii reprises his role as the Inklings from Splatoon.
Urban Legend of Zelda: There are many claims online that honking the horn just as the race starts will cause the computer players to blow their engines and have a delayed start. This is entirely coincidental; honking the horn is just a funnyEaster Egg.
When thinking up ideas for what new gameplay concepts to introduce in this game, the development team initially considered being able to drill through the ground.
In the second DLC pack, 3DS Shy Guy Bazaar was originally supposed to appear as a DLC track, but was replaced with either GBA Ribbon Road or GBA Cheese Land, as shown by its code name in the files.
This is the first Mario Kart game where no tracks (new, old or DLC) share the same music (although most parts of Mario Kart Stadium and Mario Circuit themes share the same tune, but with different instrumentation, and part of N64 Toad's Turnpike's theme is in the music for 3DS Neo Bowser City). This is broken in Deluxe, though not entirely: the music for the battle stages of Sweet Sweet Kingdom and Dragon Palace are slightly remixed variations of the music respectively for Sweet Sweet Canyon and Dragon Driftway.
As mentioned on the main page under Tomboy Princess, this is the first time where Baby Daisy now has her own animation-set for doing tricks, unlike in Wii where she reused Baby Peach's entire moveset. This also applies on a broader scale too, as her animations in Super Sluggers were also largely reused between the two princesses.
Electrodrome is, to date, the only track in the Mario Kart series to have a one-word name.note If one counts battle courses, then Skyscraper in Mario Kart 64 also qualifies.