Urchin Underpass

Urchin Underpass is a battle course that appears as one of the new courses in Mario Kart 8 Deluxe. The course is based on the stage of the same name from Splatoon and contains elements from that game, such as green and purple ink splotches scattered throughout the course that decrease vehicles' traction. There are also Mario Kart elements, such as Dash Panels. There are various paths that all loop around to the main area and several bridges. Jellyfish serve as spectators on the course and also appear on the course selection icon.

The music is a variant of the "Splattack!" theme played during Turf War matches. When there is one minute left in a match, the music will change to a variant of "Now or Never!", which is also played at the last minute in Turf War matches. This makes it the third course in the game to have a different music track during the final portion of the match (in this case, when the timer has one minute remaining), after Big Blue and Mount Wario, which play a different music track during the final segment. The music that plays during the final minute is also the only music track in the Mario Kart series that does not loop.

Just like in Waluigi Pinball, Hyrule Circuit, and Animal Crossing, the item roulette sound effect on this track is unique to this course. In this case, it is the ability slot roulette sound. This makes it the only battle course in the series to have a unique item roulette sound. In Coin Runners and Renegade Roundup, Splatoon's currency, cash, ﻿is used in place of coins.

Trivia

 * This is the only battle course from the Mario Kart games to have kanji in its Japanese name.
 * This is the only battle course not to feature any spectators from the Super Mario franchise.
 * A picture of Tanooki Mario can be found on one of the walls.
 * Despite not appearing in Urchin Underpass in Splatoon, Inkopolis Tower appears in the background, replacing a generic skyscraper present in the original game.
 * The Dutch name of this stage from Mario Kart 8 Deluxe was reused for Eeltail Alley in Splatoon 3, despite the two being completely different stages.