"Mariooooo!" Bowser howled, though he knew that the 'plumber' likely couldn't hear him now. "Grah! Let them goooo!" he spewed in fiery breath. Any father in his situation would likely do the same, though. For the source of Bowser's anger was clear to anyone who inspected the castle closely enough: the Koopalings were missing! "Pesky humans!" Bowser fumed. "It's bad enough that you stomp my minions at every turn, but now? WHY?!?"
It wasn't just Mario that was responsible, of course. This kind of operation could only be done with help, and Mario had plenty of 'friends' to help him pull a job like this, chief among them his brother, Luigi. He was likely the mastermind of this plan, Bowser realized. (It was much easier to think with a cool head once he'd spewed a few flames.) The string bean had always been the smarter of the two, but he preferred working in the background, letting Mario take the credit. Mario had the muscle and the charisma to pull off the plans that Luigi came up with, (though Luigi, interestingly, could jump higher. Must be his lighter weight, Bowser mused) and the ambition to be the leading man.
Then there were the princesses, the Mario Bros. girlfriends. Peach Toadstool, ruler of the Mushroom Kingdom and Mario's lover, had the Toads well under her thumb, and was gifted with potent magical powers that nearly rivaled her good looks. Luigi's gal, Daisy, was very much the opposite. Ruler of the desert kingdom of Sarasaland, she was very much a tomboy, and an avid athlete. While she possessed no magic, to speak of, she had the strength and skill to more than make up for it.
And that said nothing of Mario's animal allies. Chief among them was the Yoshi's, gluttonous reptiles who primarily lived on their own island, though one green one who was especially close with Mario sometimes served as his mount on the mainland. There were also the Kongs, though Donkey and Mario could hardly be called friends after that business with Pauline. She, of course, wouldn't talk to either of them anymore. He'd leave both groups alone, if he could—the ape could pack near as strong a punch as he could, and Yoshis seemed to be made of rubber!
Then there were Mario's cousins, Wario and Waluigi. Thinking about them made Bowser pause. They weren't exactly close to the Mario brothers, not that they were buddies with him, either. But if they were in on Mario's plan…they might be able to be persuaded to help him out, with information if nothing else.
That thought made up Bowser's mind as to where to go first. Waluigi lived on an island populated by Piranha Plants and a few other nasty, if neutral, creatures. And Piranha plants didn't take to well to fire, even though they liked to throw it, too. Waluigi would also likely know the security codes for Wario's factory, though whether the prankster would give them to him was another story.
Yes, the stickman would be his first objective. Bowser smiled as he left his fortress in Dark Land and began his quest…