He made his appearance with the rest of the Mario and Sonic gangs at the end of "Frightmare!".
He stuck beside the two gangs throughout most of the journey of Legend of the Eight Firstborn. When they all helped the KND battle Bowser and Eggman's minions in Chicago, he got acquainted with Fanny Fulbright, who was impressed with Luigi's Poltergeist 3000 vacuum, plus they are both firebenders that produce green fire. After the Sea Fleet stage, Luigi helped Mario and Eva battle Wendy O. Koopa. But after the battle, Luigi was hit with a Darkness Cannon, showing him a vision of Dimentio, Dimentia's brother, who talked about how Mario was stealing Luigi's spotlight. As a result, Luigi transformed into Mr. L, and told the others that he was going to get acquainted with the other villains before leaving them to battle the Multipus.