Duck Nukem

""Just something I picked up in Zanzibar, motherducker!" -Duck Nukem as he stops Mario"

- (Luigi) "You know, Duck... After all we've been through these past seven minutes, I gotta say: You truly were the real Super Mario Brother all along." "Damn... You turned this ugly duckling into a swan, Luigi!" - Duck after Luigi's emotional speech

Duck Nukem, more commonly referred to as just Duck, is the deutoragonist of the animated short movie The Blue Shell Incident, made by the Vinesauce streamer Joel.

Origin
Luigi encountered a younger Duck Nukem on Zanzibar island, the same island where Mario would let his hitman Lasagna Ocelot make an attempt on Luigi's life. Luigi fed the young duck breadcrumbs, and Duck later witnessed or heard of the attempted murder. Angered, Duck decided to one day repay his debt to Luigi.

In The Blue Shell Incident
Duck stops Mario from finishing Luigi at a bar by shooting wildly with his gun. Despite Duck running out of ammo, Mario flees the bar. Duck explains he's helping Luigi, and explains why he chose to do so. He teams up with Luigi to finish Mario and to stop him from murdering anyone.

After a mad car chase, Mario crashes into a diner. Before confronting Mario again, Luigi confesses that he sees Duck Nukem as his real brother, causing a tearful reaction from Duck as he promises to treat him to "Spaghetti on the rocks" when they're done with Mario. Though Luigi falls for Mario's "Hand-io" disguise, Duck sees through it. Mario then reveals himself to be the musician Scatman John, shooting at Luigi and Duck. Luigi flees to the sewers, while Duck stays in the diner and witnesses Mario's Scatman disguise being a fake-out.

He also sees Mario reunite with Lasagna Ocelot and call in their secret weapon, Metal Gear McQueen. With Luigi still absent, he alone aims to stop it, eventually planning to do so with a point-blank bazooka shot. Luigi attempts to stop him, not wanting to lose his new brother. Duck Nukem goes through with it, however, destroying Metal Gear McQueen at the cost of his own life.

Mario survives and challenges Luigi to a fight to the death, mocking him for mourning Duck. Luigi uses Duck's last feather as a Cape Feather power-up and avenges Duck by defeating the now-giant Mario. Mario ends up using cheat codes to spawn a Power Star, but Duck stabs him before he can do so, ending Mario for good. He reveals he used his own Power Star to finish Mario from beyond the grave, and vanishes after saying goodbye to Luigi.

In the last scene, Luigi tells the new bartender Donald Duck he reminds him of Luigi's brother, referring to Duck Nukem before going home in DK's taxi.

Trivia

 * He is an obvious parody of the video game character Duke Nukem, even having several of Duke's quotes but having some (swear) words replaced with duck-related words.
 * Like every character in the movie, he is voiced by Joel himself. Fittingly, Joel does his Duke Nukem impression and likely also made the duck noises himself.
 * He is never actually called Duck Nukem in The Blue Shell Incident. Luigi refers to him as Duck or Mr. Duck, and there is a running gag where Mario mistakes him for different birds (or is insulting Duck by purposefully doing so). Mario calls him a "terrible turkey ", "pesky pigeon" and "weird chicken".
 * He is very much an evil parallel of Lasagna Ocelot/Garfield from the same movie. Both are gun-wielding talking animals helping a Mario Brother out. Duck is much nicer to Luigi than Garfield is to Mario, however, and is noticeably more competent. However, Garfield turns out to have been working for Scatman John at the end of the movie, which may explain his unhelpful behavior towards Mario.
 * Despite his loyalty to Luigi, he supposedly works for someone else. It's never revealed who, however, as the name of the person or organisation is replaced by unintelligible duck noises.