Luigi is Mario's younger brother and a main protagonist in Super Smash Bros. Crossover. He still retains his traits from the games. In Season 4, Psycho Kirby explained his origins to a brainwashed Luigi, which motivated Luigi to free the others from the mind control. At the midway point of Season 5, Luigi and everyone else, including the villains are defeated by the Dark Smashers. In Season 6, Luigi battled Ganondorf and won. In Season 7, Luigi is ambushed by Magneto and engages him in battle but the fight is short since Magneto retreats due to Drago being vunerable. In Season 18, Luigi is infected by the zombies, as Mario mentions trying to find food for him and Princess Peach. Luigi is later killed by Yami Bakura along with Peach, and his hat is taken by the evil spirit. Luigi is later revived as one of Yami Bakura's reanimated soldiers. Oddly, Luigi is uninfected despite dying as such, and his hat has returned to him. Luigi gets revived by Shenron at the end of Season 19. Luigi moved to Smash City with Mario in Season 20, and teams up with his younger self during the Time Eater Arc. In Season 22, Luigi registers for the Neo Smash Champion Tourney as a member of Team Lucario along with Princess Daisy and Lucario. Luigi and his teammates later wind up battling against Team Meta Knight, consisting of Meta Knight, Link, and Toon Link, and is forced to reveal his Ascent Mode in order to survive against Link and Toon Link's Ascent Modes. In Season 23, Luigi and Baby Luigi team up with their retro counterpart to fight against Coredegon, Slycerak, Exostriker, and Mandibor. At the end of Season 25, Luigi becomes a Hero of Legend along with his brother.
Retro Luigi is Luigi as he appeared in the original Super Mario Bros. Retro Luigi first appeared in Season 23 along with Retro Mario exploring the White Space, where they meet up with their past and future selves. However, they hear Dr. Eggman's voice, prompting Retro Mario and Retro Luigi to go after it. The Retro Mario Bros. then see Classic Dr. Eggman, who dispatches Modern and Classic Metal Sonic on them. Luckily, the Retro Mario Bros. gain assistance from their past and future selves. After defeating Metal Sonic, the Luigis stay behind to fight Retro Bowser.
Luigi's appearance is based off his modern day appearance. In Ascent Mode, Luigi wears his Fire Luigi outfit.