That whole castle thing is wrong though.



Level 1-1 has no castle. Because Mario is just showing up.



The end of level 1 has a small castle. The beginning of 1-2 has the same castle. (You see it in the cutscene as Mario enters the pipe.) And the end of 1-2 also has a small castle.



You see this castle at the beginning of 1-3.



At the end of 1-3 you get a giant castle.



In 1-4 you're in the castle.



And at the beginning of 2-1 and all other x-1 levels you have a large castle at the start because you're exiting it.



It's consistent and standard across the whole game.



Once the loop is in effect you see Large, Small, Small at the start and Small, Small, Large at the ends of every level. The castle isn't shrinking or anything. It's just drawn the same to save on memory. It's just the CloudBush syndrome. Reuse sprites and patterns to save space in memory.



It's a window at the top. But could very well be a door too since it is indeed a balcony up there.



The part people should be wondering about is how the large castle wall continues on infinitely if you manage to jump over the flagpole and keep running. But if you just finish the level normally, the next x-1 only has the large castle itself and not the infinite wall. Memory restraints! The last tile of the level repeats for some reason. Instead of just stopping the camera. Why? I mean 1-2 (Underground) has a camera stop position if you go to the Warp Zone. But when above ground the level extends forever if you happen to make it over the pole. Such a weird thing.