Here is an overview of the game, via Arc System Works:
■ What is Downtown Rantou Koushinkyoku Mach!!?
Downtown Rantou Koushinkyoku Mach!! is an enhanced version of River City Melee: Battle Royal Special with new elements added that make for more heated battles.
New Item: “Bamboo Shoot”
The player that eats it will become gigantic!?
New Game Mode: “Change Match”
A battle mode where defeated teammates change characters on the spot. There may be also special gimmicks depending on the stage.
New Element: “Team Edit”
Assemble your favorite characters to create a dream team!
Other new elements will also be added! Look forward to more information in the future!
Downtown Rantou Koushinkyoku Mach!! actually first debuted during the Japanese version of the February 13 Nintendo Direct. Watch the first footage from 0:17 to 0:24 in the video below.