At first, you'd think that Mario would just go into a Warp Pipe. But wait! Remember the Koopa Cruiser from M&L? Also, what about the Cape and the Super Leaf? Don't forget Jugem's Cloud, and many that I've probably left out (like FLUDD).
So, how does Mario get from kingdom to kingdom? Why the Koopa Cruiser, and not just the Pipe? There was one right in Stardust Fields, not to mention one right in Beanbean Castle Town.
Also, why doesn't Mario just warp straight to Bowser's Castle? Please reply, I need other people's view on these things!