Well, that was believable, but what does TTL’s SMB3 look like?
For that, please take a look...
One day, while celebrating the end of Bowser's capturing, a new enemy entered Peach's turf. It just so happens that this new enemy is a French materialistic rabbit named Madame Broode, who kidnaps Peach to be her modeling slave for her lavish endeavors.
Mario and Luigi immediately jump into action, while Toad reopens his Item Shops whenever they may need them. As such, you can give him the option to become the Player 3 of this game. This won't be easy, though, as Madame Broode also has her working staff, the Broodals, as bosses for each world.
Speaking of Toad, there is an option for him to become their Player 3 once you reach the second Toad House in the game. Not only that, but after completing World 5, Peach somehow saves herself by tricking Madame Broode into letting her go, by asking if she can take a bathroom break. You see, Madame Broode actually cares about giving her models enough to live. It might be the bare essentials necessary, but she does care.
From then on, you can play as either Mario, Luigi, Toad, or Peach for Worlds 6-8, including the boss battles, which also includes the battle against Madame Broode herself. In fact, if you do this as Peach, she'll get even angrier at her than the other three of them.
Once you go to Broode's hangout, you'll actually see Bowser guarding it, who contracted the Broodals to kidnap Peach in exchange for her ownership after she models for them. Which is ironic, given how you can make Peach's playthrough more awkward by having her go straight past him when he least expects it.
Finally, Madame Broode appears, and after harming her three times on the head, she collapses and gives the deed to Peach back to the four of them.
After that, the celebrations can continue. And, as an added bonus to finishing as Peach, Bowser enters the castle asking for forgiveness and to genuinely befriend them for once. They begrudingly agree to this, on the condition that Bowser can't directly kidnap the princess ever again. He agrees to this, and they're all right as rain now.
Due to the ending being like that, this explains why Bowser is almost always part of the spinoffs, like Mario Kart and Mario Party.
What do you think?