Project Thunder: Saving Juliano
Mario's Crew and Rodney's Crew go to Mount Nexus to pick up Juliano, and in the process they get to meet the local versions of his original family. It goes pretty smoothly up until they're about to give him the Meme cure, at which point Mr. L crashes the party and takes him away, leading to a wild chase through all the different CC:TG worlds where the Rising Star Circus crew proves fully capable of keeping up with the others, and actually work surprisingly well with them.
It eventually leads to a big brawl against an army of Brobots and Twilight monsters in the papercraft cityscape Mr. L added to the game for himself, where he reveals Super Brobot, a version of the original Brobot M-Type that has a whole giant body under the giant head. There's also Reboot Saiko in all her insane razor-sharp glory, but she's focused almost solely on her counterpart so it's not that big a deal. Also, Mario and Luigi at one point manage to fuse, the result calling himself Jumpman, and make the fight against Brobot an even 2-on-2 duel on top of a half-constructed skyscraper.
He wins, but Brobot explodes when defeated, which bursts the fusion and sends all four people involved flying. Luigi manages to catch Juliano and get him to the ground intact, while Mario and Mr. L crash on a nearby rooftop, Mario disoriented from both the explosion and the post-fusion hangover. L pulls a gun, ready to finally take his revenge once and for all, since it won't destroy the SM64 universe anymore thanks to Elanore and it wouldn't even matter if it did because he moved out...
...but he can't do it.
The one thing he thought he wanted more than anything from the moment he was created, and he can't
fucking
do it!
What's stopping him!?
While he's struggling with himself, Mario looks up at him, still really not all there, and asks, "Lu, you okay?"
Oh.
That's why.
L hurls the gun to the ground and points accusingly at his brother, "One time. You get one!"
And then he opens a portal and leaves, already thinking of possible ways to purge the last of Luigi's influence from his dark heart.