- "Oh, me? Just one of Count Bleck's more promising minions. The Green Thunder... MR. L!"
- ― Mr. L
Mr. L was created when Luigi was hypnotized by Nastasia and inducted into Count Bleck's army. Mr. L was sent on an assignment during the events of Chapter 4 to defeat Mario, the hero of the Light Prognosticus. Mr. L appeared in front of the heroes after complementing and jumping on Squirp and challenges them using the Brobot, a robot made to look like Luigi's head. Mario was able to defeat Brobot and his pilot, forcing Mr. L to retreat.
Later, Mr. L, along with Mimi, attacked Mario in the ruined Sammer's Kingdom. Mr. L was defeated, and during his escape he was attacked by the scheming Dimentio who sent him into the Underwhere. During the attack, Mr. L reverted to Luigi. Luigi had no idea how he arrived in the Underwhere and in fact had lost all of his memory about his time as Mr. L.
At the end of the game, Luigi is transformed through the power of Dimentio who hypnotizes Luigi using a Floro Sprout and mixing him with the Chaos Heart, transforming Mr. L into Super Dimentio. He was then defeated for the third time by Mario, Peach and Bowser.