General Details
The art style is cartoonish and full of life and color. It's said to be reminiscent of Hotel Transylvania in terms of style but Mario.
The action is said to be really well choreographed. They brought up the Donkey Kong fight from the beginning and said that it was quite fast paced even "blink and you'll miss" at times especially when Mario gets the Golden Hammer.
The humor in the movie is said to be very punny/meta, not everyone will like it but on a positive note no dabbing or fart jokes etc.
For character design Mario and Luigi have slight changes. They start off the movie with worn and dusty clothes with a bit of a muted color scheme, Mario has a blueish purple shirt instead of brown and Luigi has green overalls and a blueish purple shirt as well. As time goes on they switch over to their more iconic colors.
Mario and Luigi have Brooklyn accents in this movie.
As for character appearances (other than the main cast of heroes/villains), DK Jr. Pauline and Toadsworth are said to appear. Daisy is name dropped. There are some female Toads too but none specifically called Toadette. There is also a character named Spike who shows up at the beginning of the movie and is this kind of greedy/bossy (but not villainous) character who also shows up at the end to congratulate them.
There are a number of different enemies in the movie, Goombas, Koopas, Hammer Bros, Buller Bills, Banzai Bills, Lakitus, as well as Fuzzies and Ninjis were mentioned.
Plot Outline
The movie opens with a narration by Charles Martinet as we go through the different jobs Mario has had over the years before joining the wrecking crew. He saves the Mayor from Donkey Kong in the "real world" New Donk City.
In the present day Mario is quite famous. When he hears about reports of Gorillas and Turtles fighting in the sewers he goes to investigate. Underground there are a ton of Gorillas, some partying, others playing drums. Here he runs into an older cranky Donkey Kong but can't communicate with him because he speaks Gorilla. They end up falling through a pipe teleporting them to Mushroom Kingdom.
At some point near the beginning we hear the first "song" of the movie. Here Bowser sings as we see his younger years/desire to take over Mushroom Kingdom. He then kidnaps Princess Peach, blows up Mushroom Kingdom and then heads for his ship. Mario and Captain Toad go on a journey to stop Bowser.
The second "song" of the movie is about plumbing.
At some point, Luigi is concerned because Mario has been gone for quite some time. He goes to the sewers but ends up in Mushroom Kingdom, the Forbidden Forest specifically, where he runs into Yoshi.
Mario goes to fight Bowser but is beat down quite badly. Kamek drops him off the ship into the Forbidden Forest where he meets with Luigi and Yoshi and likely at this point is when they get their new costumes with more iconic colors.
They head to Bowsers Castle and at some point they come across these 3 Bowser Clones. These clones mostly tell jokes but once they are defeated they shapeshift into this indescribable combination of enemies.
The final "song" happens at some point before the final battle and basically everyone sings here. The Toads sing about saving the princess, Mario and Luigi sing about not losing hope, Bowser and Peach argue to the beat of the song.
In the end, Kamek gives Bowser a mushroom that causes him to grow. He chases after Mario and Luigi as they run through a pipe maze across different locations (a desert, ocean, forest, and cloudy area were all mentioned). Power ups like the Fire Flower and the Star make an appearance at this point of the movie.
Yoshi has some history with Kamek (I believe it was mentioned that Kamek was the one who exiled him to the Forbidden Forest?) so they end up fighting. Kamek uses his want to mess around with Yoshi altering the environment.
At the end of the chase they trick Bowser into going through the last pipe, straight into his own lava pit.
After all is said and done Mario decides to open up a plumbing service in the Mushroom Kingdom.
Post credits scene is Bowsers skeleton...
