Mr. L

"The Green Thunder strikes like lightning!"

- Mr. L

Mr. L, also known as The Green Thunder, is Luigi, brainwashed by Count Bleck's assistant, Nastasia in Super Paper Mario. After Luigi tried to escape Count Bleck's Castle, Nastasia caught him and brainwashed him. Before Mario could get his hands on a Pure Heart, Mr. L made his dramatic appearance in the Whoa Zone (complete with stylish poses). He decides to fight Mario and reveals himself as one of Count Bleck's new minions. He attacks with a super jump and can use an unlimited supply of Shroom Shakes to heal himself in battle.

When he is bested in combat, he reveals his trusted giant-robot "brother", Brobot, which he attacks Mario with in space. Using Squirps, Mario shot down Brobot. When he was defeated, he vowed to return. Later, at Count Bleck's lair, Mr. L did not seem pleased with Bleck's other minions, going so far as to call them "junior" minions and calling them weak.

He returned as a boss in Chapter 6, after the dimension was destroyed by The Void. Here, he fights with Brobot L-Type. After being defeated, Dimentio betrays him and attempts to kill him. After being sent to The Underwhere, Mr. L turns back into regular Luigi and forgets that he ever was Mr. L. Later though, before the final battle, Dimentio tells Luigi that he was indeed Mr. L, and activates a Floro Sprout he had planted in Luigi's head to brainwash him into villain once more.

Trivia

 * He gets a mention in Super Smash Bros. Brawl in Paper Luigi's trophy. It oddly refers to him as "Mister L", instead of the proper "Mr. L."
 * During the battle with him (outside of Brobot) the player can use Thoreau to grab the Shroom Shake that Mr. L is about to use and use it on the player itself for 10 HP.
 * The name Green Thunder may come from the fact that Luigi has the Thunderhand in Mario & Luigi: Superstar Saga, but this is unconfirmed.