NOTE: This spoiler was submitted by Jeremy

The film starts in an ice kingdom of blue penguins where a large menacing ship belonging to the Koopas. Once they land, the Koopa army emerges to confront the penguins. Kamek (Kevin Michael Richardson) comes out to introduce their king, the sinister Bowser (Jack Black). While the penguins attempt to (pathetically) fight back, Kamek uses his magic to throw them to the side before Bowser unleashes his fire breath to melt the penguins’ ice castle. He then goes to a box with a question mark and crushes it, revealing the Super Star. Bowser then boasts that there is nobody who can stop him.

In Brooklyn, brothers Mario (Chris Pratt) and Luigi (Charlie Day) are watching a commercial for their new plumbing business. They get mocked by their ex-boss Foreman Spike (Sebastian Maniscalco), but Mario steps in to defend his brother since Luigi is nervous and easily afraid. Moments later, the brothers get a phone call for their first big job. Unfortunately, their van breaks down, forcing them to run across a construction site to make it to their destination.

The brothers arrive at the home of a wealthy couple, where Luigi already makes a bad impression when he steps on the toy of the couple’s dog, Francis. Mario quickly fixes their leaky faucet, but Francis goes after them. This leads to the bathroom getting more wrecked and Francis nearly falling out the window until Mario and Luigi save him.

The two return home where they live with their family and are having pasta with mushrooms (and Mario hates mushrooms). Their parents don’t have faith in their plumbing business and write it off as a silly dream, leaving Mario dejected. Luigi goes to comfort his brother, who says he wishes he didn’t always feel so small. They then see the news that there is a massive pipe burst in downtown Brooklyn, and Mario thinks only he and Luigi can fix it.

Mario and Luigi make it underground as the streets start to get flooded. They find the source of the problem and start to climb their way to the main pipe, but they end up falling deeper into the sewers until they come across a system of pipes. The brothers get pulled in through one of the pipes and are taken through portals, where they are separated.

Luigi ends up in The Dark Lands, where he is found by skeletal Koopas called Dry Bones. They chase him until he runs toward a castle where he thinks he is safe until little masked minions (Shy Guys) end up capturing Luigi.

Mario ends up in a land full of giant mushrooms. He meets a little mushroom-headed creature, a Toad named…Toad (Keegan-Michael Key). Mario explains to Toad that he got separated from Luigi, and based on his description, Toad figures Luigi is in The Dark Lands. He guides Mario to The Mushroom Kingdom so they can get help.

Mario and Toad arrive at the castle of Princess Peach (Anya Taylor-Joy). She knows Bowser is a threat and is making plans to face off against him with the help of the Kong army after he took the penguins, prisoner. Toad helps Mario sneak into her castle, and Peach is ecstatic to meet another human. Mario asks for her help in finding Luigi, and she says she will once she sees what he is made of.

Peach shows Mario an obstacle course that he must go through to prove himself. She does it effortlessly in one go, and she shows him the power-ups that he can use, but unfortunately for Mario, they’re mushrooms. He eats one that makes him bigger and stronger, but whenever he gets hit, he loses the power-up. Mario endures hours of falling platforms, man-eating flowers, and wrecking balls. On his last try, he nearly makes it before the flower chomps on him, but it’s enough to convince Peach that Mario can help fight Bowser. Peach departs from the Toads as they head to the Kong Kingdom, but they are joined by Toad.

Before their journey, Peach demonstrates an ability to Mario to produce fire using a flower. He asks where she came from, but Peach isn’t sure. She remembers coming to the Mushroom Kingdom as a lost child, and the Toads raised her before making her their princess.

Aboard the Koopa ship, Bowser explains his plan to marry Peach and rule together with her using the Super Star. Later, Bowser sings a piano ballad to himself before Kamek comes in to inform him that Peach has been spotted with Mario, making him super jealous. The Shy Guys bring in Luigi, whom Bowser tortures (yanking his mustache hairs) for information on his brother.

Mario, Peach, and Toad arrive at the Kong Kingdom to speak to Cranky Kong (Fred Armisen) over gaining his army to fight Bowser, but he refuses. Mario steps up, determined to save Luigi, so Cranky agrees to help on the condition that Mario fight Cranky’s son in the arena and win. Mario agrees, despite Peach saying it’s a bad idea.

In the arena, Mario is pitted against Donkey Kong (Seth Rogen). Naturally, the much smaller Mario initially gets whooped by DK, until he starts to take advantage of power-ups. His first attempt goes poorly when he eats a blue mushroom that makes him tiny. He then gets another power-up that gives him a cat suit, which allows him to use cat-like reflexes against Donkey Kong. The ape throws barrels at Mario, but he dodges them and uses his power to punch DK down below, defeating him. Cranky agrees for the Kong army to help Peach.

Luigi is imprisoned alongside the penguins and their king (Khary Payton), along with a cheerful (but grim) little star called Lumalee (Juliet Jelenic). Bowser also learns about the Kongs’ alliance with Peach, and he plans to stop them.

The heroes assemble karts to go after the Koopas. They ride across Rainbow Road to head after them, but Bowser’s army ambushes them. The Koopas attack, but Mario and the others are able to fend most of them off. Toad almost falls off but Peach rescues him. A Koopa General (Scott Menville) tries to use his rig to kill Mario, but he avoids the attack and blows up the General’s vehicle. The General gets angered and activates his blue shell, performing a kamizake attack that destroys part of the bridge and sends Mario and Donkey Kong falling into the ocean. The Kongs are captured, and Peach rushes back to the kingdom with Toad to warn everyone.

Mario and DK argue as they fall into the water, but DK is knocked out by a falling kart tire. Mario saves him but they are both devoured by a gigantic Maw-Ray. They find a rocket from DK’s cart and use it to blast themselves out of its stomach and on their way back to the Mushroom Kingdom.

Peach returns to get the Toads to evacuate, but Bowser and his goons show up. He offers his proposal to Peach, who immediately refuses until Bowser orders Kamek to torture Toad. Peach then agrees as long as the Toads are unharmed. Kamek then goes to the other prisoners to announce that they will be sacrificed.

The wedding ceremony is about to go off until Bowser presents the sacrifices. Peach then says she was never going to marry him and takes in a blue flower to give herself ice powers. She freezes the mechanism and Bowser while the Toads begin to fight the Koopas. The mechanism breaks apart and the prisoners are lowered further into lava, with Luigi nearly dying first until Donkey Kong arrives, having been powered-up with Mario, to raise them back up. Luigi falls until Mario shows up in a Tanooki outfit that lets him fly. Bowser breaks free from the ice and orders a Bomber Bill to be launched at the Mushroom Kingdom to obliterate it. Mario flies in Bill’s eye and gets the giant bomb to chase after him, leading him to the portal pipes where Bill explodes. The ensuing explosion causes everyone in the kingdom to get pulled in.

Everyone ends up back in Brooklyn, including the Koopa ship. A now enraged Bowser attacks Mario and beats him down, saying he has no chance to stop him. While Peach and DK try to fight, Mario hides in the pizzeria and sees his commercial with Luigi, inspiring him to keep up the fight. Bowser loses the Super Star, and Mario tries to grab it, but Bowser lets out his fire breath until Luigi steps in to shield Mario with a manhole cover. The two then run to the Star and touch it, making them invincible and powerful, officially becoming THE SUPER MARIO BROTHERS! They plow through the Koopas and proceed to kick Bowser’s butt before slamming into him together and annihilating his ship. Now weakened, Peach feeds Bowser a blue mushroom to turn him tiny, and Toad traps him in a jar. Mario and Luigi’s parents, the people of Brooklyn, and even Spike cheer for the brothers for saving everyone.

Later on, Mario and Luigi continue their plumbing business, only they are now residing in the Mushroom Kingdom. The brothers hop into a portal pipe for another adventure.

Mid-Credits Scene: Tiny Bowser tries to sing a song in his cage before Toad tells him to shut up.

Post-Credits Scene: In the sewers of Brooklyn, a little egg with green spots begins to hatch, and a little voice calls out…”Yoshi!”

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Beloved plumber brothers Mario and Luigi are sent from Brooklyn to a new world after getting pulled through portal pipes. Luigi ends up in The Dark Lands as a prisoner of the menacing Koopa leader Bowser. Mario teams up with Princess Peach, Toad, and Donkey Kong to fight back and save Luigi.

After Mario goes through some training and fights and defeats DK in the arena, they use karts on Rainbow Road to go after Bowser, but his Koopa army ambushes them and captures DK’s people and father. Mario and DK team up to save their friends while Peach and Toad go to warn the kingdom.

Bowser tries to get Peach to marry him, to which she only agrees so he won’t hurt the Toads. The heroes then save Bowser’s prisoners and fight his army, and they get sent back to Brooklyn where Mario and Luigi get powered up to defeat Bowser and his army, and Peach shrinks him down to be imprisoned. Everyone regards Mario and Luigi as heroes, and they stay in the Mushroom Kingdom.

The end credits implies Yoshi is being hatched in Brooklyn.