One morning, Mario and Luigi are at their house getting ready for Princess Peach's birthday. When all of a sudden, Mario hears Bowser's Airship fly across his house towards Peach's Castle. Mario looks out the window, gasps, and then wakes up Luigi. (He was sleeping still). Luigi refuses to get out of bed, and Mario grabs Luigi by the head and slams his head on the window. Luigi's eyes pop out and Luigi screams when he sees Bowser's Airship go to Peach's Castle. The Bros. run out the door of their house and then it switches to Bowser on his Airship.
"MUAH HA HA HA! Koopalings! Are you ready for the ambush?" Bowser says.
"Yes we are! Let's kidnap the princess!" the Koopalings say. (including Bowser Jr.)
Bowser and the Koopalings then get in their clown cars and the Koopalings use their magic to ambush the castle. Then it switches to a weird figure holding some sort of powerful staff watching Mario and Luigi run towards the castle while it's being ambushed. That figure says, "I finally found them..." Peach, inside the castle with the toads, gets a pet cat for her birthday and names it Lario. When then, Bowser and the Koopalings break in through the ceiling and walls. As Peach and Toads get shocked and panic, the Toads flee while the Blue Toad hides behind the throne. Mario and Luigi then burst through the castle doors with an epic entrance. Bowser points at Mario and Luigi, and the Koopalings, still in their clown cars, advance towards them. Mario and Luigi jump on their heads, and they get all dizzy with the stars above their heads and stuff. Mario and Luigi run towards Bowser and Bowser Jr. only to realize that it's cardboard cutouts of them! They then look to the right and see Bowser and Bowser Jr. laughing while Bowser holds Peach and Bowser Jr. holds Lario. But then, the shape of a cat's face outlined in purple becomes visible near the wall Bowser, Bowser Jr., Peach, and Lario are next to. Then that wall explodes and the people who were next to that wall fly in the air. Mario looks at Luigi and nods his head. Mario then jumps and catches Lario, while Luigi jumps and catches Peach. Bowser slams into the throne chair and knocks it over. Blue Toad realizes his hiding place got destroyed and runs behind Mario. Bowser Jr. falls on the ground. While Bowser and Bowser Jr. are unconscious, the smoke at the exploded wall clears up and shows WART holding a dark staff with a kitteh's face on it. Everyone gasps when see Wart.
Wart says, "It's been a while Mario Bros.! Great to see you guys are doing good! Anyways, I got big plans, so let's get this overwith shall we gentlemen?
Mario gives Lario to Blue Toad, and then Mario gets in an angry, fighting stance.
"What's this? Hm, I don't feel like playing dirty right now, so I might as well lock you guys up." Wart says as he points his Cat Staff towards the ceiling.
The staff shoots a purple laser, and a dark cage with a cat face on it falls on Mario, Luigi, Toad, Peach, and Lario. Those cages also fall on Bowser and the Koopalings.
"Well, it was great seeing you guys again, but I gotta go. Ta-ta! Minions! Take Bowser and his henchmen on our Airship. Hm? What's this? A cat? Ah, he'll make the perfect pet for my cat kingdom!" Wart says.
"No!" Peach yells.
"Hm, I guess I'll have to take him by force!" Wart commands.
Wart's staff lights up and a laser shoots Lario then brings Lario to Wart.
"Enjoy being locked up Mario Bros.! Haha!" Wart says as he leaves holding the cat in his slimy arms.
"LARRRRRIIIIOOOOOOOOO!" Peach yells.
Soon after Wart's Airship takes off with Bowser, Bowser Jr., The Koopalings, and Lario held captive, Toadsworth and the other Toads break the lock on the cage and Mario, Luigi, Blue Toad, and Peach are set free. Peach runs outside, acting as if she can pursue Wart's Airship when it had already taken off a while ago. Mario, Luigi, and Blue Toad decide to follow her, and the first level/tutorial/or whatever begins. XD This was way longer than I thought .

Bowser has terrorized Mushroom Land again, it's up to you to beat him.