The Wheel Thing
Mario and Luigi are enjoying a quiet day sitting on the front step of a random house, watching the cave people pushing boulders around and rowing boats on land, which is apparently considered not only "working", but "working too hard." After thinking of a way to help them out, they set about cutting some wheels for them, only for Kooky Von Koopa, the mad scientist of Bowser's offspring, to spy on them.
Mario takes the wheels to Ugga and Ooga, who are carrying a crate full of stones, and rolls the wheels at them with the message "give your backs a break," which to cave men, is the equivalent of "use them as pillows for three seconds and throw them in your crate." He then groans and tells them to use their heads.
"Ooh, booga boofa."
When you hear that, you know you've made some mighty fine hats.
Luigi tries giving some wheels to Yoshi (why he bothered and why Yoshi is fishing isn't explained), who eats them purely out of instinct, while Ugga splats a bug with the wheels. After using a fire flower to knock a stack of wheels down for no reason and Yoshi trying to eat the fishing rod, Mario finally shows them how the wheels work, and Luigi gets himself a prehistoric skateboard, which doesn't last terribly long until Yoshi, looking more stupid than ever, hops on his back and causes him to crash, and eats the skateboard.
The Princess is then shown Mario's new car making factory, where the construction of one involves the work about seven people, plus one Goomba for each car to make the things run. Despite Mario's enthusiasm, Peach believes that they're advancing too fast, and Luigi cracks the obligatory gag to say his view on the matter. After a brief teaser at Bowser's castle where Kooky is shown making his "most monstrous invention ever", Luigi continues telling Mario how the cave people are simply crappy drivers and they're in serious need of some order and rules on the road. Mario shrugs it all off and jokes "what are they gonna do, banish up to the lava pits?"
"Okay, so they banished us!"
Elsewhere, Kooky shows his pop his new invention, Mega Mechanasaur, which is just like the cars except it's a giant robotic dragon that uses a tiny dragon to breathe fire and a dinosaur on a treadmill to move it, and they set about running over various buildings and cars. I feel the need to point out that you clearly see the drivers escape and none of the cave people are harmed, but you never see the Goombas escape. Every last one of them are squished by Kooky's contraption. That's just morbid. Ooga, just after having his ride trampled, heads to the Princess and gives her the 411 on everything.
Thus ensues another awkward scene where the Mario Bros. happen to not starve because Mario had his "emergency pizza stash" on him, and Mario decodes the Princess's Morse code message sent by a pipe telling them to get back and sort everything out (thus meaning if they were banished yet could leave at any time, what's the point of being banished in the first place?). However, the smell of the pizza attracts a Blargg which chases them around for a while until, with the help of a spring delivered by Peach, gets a Cape Feather and flies them out of the pipe.
While Kooky and Bowser are continuing to cause destruction, Mario and his factory prepare to funk up the shiz of the monstrous robot thing with traffic lights, barriers, and Yoshi wearing a shovel on his nose to make potholes.
Awkward song time! With the power of traffic lights shooting fireballs and Yoshi digging potholes big enough to pull off wheels bigger than himself, they total the evil machine, sending the bad guys off to rethink their plans.
Despite kind of causing the whole turmoil in the first place, both of the car crashes and Kooky getting ideas, Mario, Luigi and Yoshi are tossed into the air by the cave people while they decide to hold off on the wheel thing for a few thousand years, and Yoshi licks them simply because it makes a good end to an episode.
When the cave people are bickering at the huge car crash, it almost sounds like one of them says the f-word. NAIVE HILARITY!
As I mentioned, none of the Goombas in the cars are seen escaping, yet the dinosaurs running Kooky's machine are seen fleeing.
After setting up the car factory, Mario spends all his time sleeping until he's nagged at by Luigi and then banished. Just like a real business man!