Luigi is in Super Mario Bros. 35, but Mario's taller, shyer brother won't enter the spotlight unless you complete a specific set of actions. It's typical of the green-overalled hero, who's occasionally an afterthought in the Super Mario series.
Earlier today, Twitter user and illustrator CombotronRobot showed off footage of Luigi in Nintendo's new Super Mario battle royale game. They initially seemed uncertain of what made Luigi appear other than the involvement of the L button, which they held while starting a match. They also noted they're "Star Rank," which requires you to reach level 100.
A Nintendo Switch subreddit thread is currently trying to deduce the exact science necessary to make Luigi show up. It's since been determined that you need to have all of Mario 35's stages unlocked as well.
You also need to lean in on pressing that L button. "Hold L as soon as you've selected the stage. Keep holding until the match starts," writes redditor "cso88ex." They also remind other players that starting a match with the Fire Flower results in Luigi using the same sprite as Fire Mario. This tracks, as Fire Mario and Fire Luigi share the same sprite in Super Mario Bros. Hey, when you have 31 kilobytes of memory to work with, you have to cut a few corners.
Super Mario Bros. 35 is unique take on the battle royale genre, and I find it a lot more fun to play than games that invite you to kill 'em all in a more traditional manner, e.g. shooting your foes in Fortnite or PUBG. It's free to play if you have Nintendo Switch Online, but Nintendo has plans to pull it off the service after March 31, 2021. Dress up as Luigi and Smash ye rival Marios while ye may.