While playing with Fishy Boopkins and Shroomy at Peach's Castle, Luigi's doll suddenly gained life and appeared in the corner of the foyer. When Luigi tried to retrieve it, it became sentient and attacked Toad, transforming him into a Luigi Doll. Apparently, the original Luigi Doll was mad at humanity for their crimes committed against them, being treated as abominations, slaves, and animals, and was preparing an uprising. Luigi, not wanting a repeat of the first invasion, fled with Boopkins and Shroomy to an ice cream shop. SMG4 forced them to open the door to no avail. Boopkins promised to avenge him as two Luigi Dolls infected SMG4, much to his horror. Locking themselves in a freezer, they were frozen. During that time, the Weegees proceeded to usurp the Mushroom Kingdom, transforming all the citizens into Weegees and successfully usurping the kingdom for 500 years (in which they had overthrown the monarchy and the government, effectively turning the Mushroom Kingdom into a republic ruled by them). E. Gadd's descendants tried working on time machines to go back in time to stop the invasion from occurring, eventually creating a working machine, but the Weegees killed them before they could use it. New Super Duper Mario Plus Ultra (NSDMPU), Mario's descendant, and Danny DeVito were the only survivors of the catastrophe.
Finally, during the 500-year anniversary of when they took over the kingdom (hosted by Hokage Weegee, a Weegee wearing a Hokage hat from the Naruto series) in 2519, Luigi, Boopkins, and Shroomy were freed from their icy tombs in the ice cream store and roamed the land that was once their kingdom. Hokage Weegee also stated that the day marked the end of Luigi, who was their oppressor and creator (which Shroomy called "one hell of a family reunion"). Realizing their friends are all dead, the trio mourned them, but Luigi, wanting to be strong for Mario, said there must be a way out of this. Unfortunately, he ended up giving his position to the Weegees. The trio was saved by NSDMPU, who took them into his car and drove them to his hideout. Luigi could tell he was related to Mario due to his love for spaghetti and eventually told him what happened before.
NSDMPU told the gang about how E. Gadd's descendants tried to build a time machine back to 500 years ago, managing to make a working machine, but the E. Gadd Labs building was overrun with Weegees before they could put it to use. They, however, had a plan: Luigi would pretend to be a Weegee Doll, have Boopkins sing a terrible song that would distract the Weegees over the radio, and while this was happening, Luigi would allow the rest of the gang into the building, and then they would use the time machine. The plan worked, but upon activating the machine, the Weegees discovered what was going on and tried to break into the time machine room. While NSDMPU held the army off, Luigi, Shroomy, and Boopkins were sent back to 500 years ago, but not before Luigi stated that he would remember NSDMPU as his future grandnephew was killed by the Weegees.
After being sent back to 2019, the trio stopped Defective Weegee from attacking Toad and pinned it down in the Bob-Omb Battlefield room, where it explained its reasons for wanting to usurp the kingdom. Before it could go any further, Shroomy grabbed a shotgun and destroyed Defective Weegee with it, returning everything to its previous state and undoing the future timeline. With no memory of what happened, the trio continued playing with their dolls, with Boopkins' Squidward Tentacles doll kissing Luigi's doll, ending the episode.
When Shroomy points out how convenient the time machine's existence is, the camera shows a Weegee-ized version of SMG4 along with a computer reading "Script", breaking the fourth wall.
Another fourth wall break occurs when Shroomy hits the rewind limit and says that it was convenient that that point was where they needed to go, with the SMG4 Doll with a laptop, threatening to stab Shroomy.
If New Super Duper Mario Plus Ultra is a descendant of Mario, then he should be referring to Luigi as his great-uncle, not his great-grandpa, knowing that because Luigi is the younger brother of Mario.