Trapdoor to Bowser in the Dark World
The entrance to Bowser in the Dark World is deceiving. In a casual playthrough, the entrance appears to be a painting of Princess Peach, but upon approaching it, the painting changes to an image of Bowser--Mario is thwarted by a trapdoor in the carpet, leading to the stage. (There is no level geometry beyond the trapdoor and the Bowser painting itself has no entrance.)
Reverse Spawning Displacement
Because the trapdoor is directly over the warp to the stage, Mario can still be standing on it on the frame that he warps, which can lead to spawning displacement in Bowser in the Dark World if the trapdoor loaded into a sufficiently-high object slot. Mario is displaced horizontally 300 units in the Z direction, and will land on the expected starting platform, close to its right edge. This 300-unit displacement is inherited from a revolving elevator platform's initialization. Revolving elevator platforms are initially spawned at their axle, and then given one frame of translational velocity to snap them to their intended positions before any revolution regins. Thus, Mario inherits a fixed translational displacement, not rotational displacement.
The first confirmed method of manipulating the trapdoor into a high object slot (slot 102) is to visit the basement, generate dust, and return to the lobby.