Reminder : The game manage the entrances of each area thanks to header block 6 (HB6), each entrance is 20 bytes long, thus for one given area the length (in bytes) of HB6 is equal to 20×number of entrances.

http://nsmbhd.net/thread/1823-area-overflow-bug-going-to-any-level-of-current-world-area-overflow/

This is pretty much the same modus operandi but with one twist :
_Once your done with the settings, close the level and open it again but with Hex Edit this time;
_Go to block 6;
_(not mandatory but will ease your work) Resize the window horizontally so each row has 20 bytes of data;
_Go to the row corresponding to the entrance you want to modify;
_Now go to byte 12* , and choose one of the following values:

_Save

*Note : I consider the first byte (beginning to the left) as byte 1, not byte 0.

For example, if you set a door in W8-Final Castle with connected pipe id = 9, destination area = 3 and a destination world (byte 12) = 2, Mario will end in the boss area of W2-Castle.
And now you can use this useful feature to set up, for example, a Boss Blitz for the Final Castle.

Hmm, there seem to be multiple similar entrance things. I'm not sure which are the same thing and not sure which are glitchs or which were programmed.

The area overflow bug is something else: it's when you put an area number greater than the area count in the level, then the destination overflows into the areas of the next levels.

I think this is not the area overflow bug, but a feature that's coded on purpose in the entrance code and not really used in the final game. I remember seeing something like this in the code a while ago.

I noticed this earlier too. I wonder if this could make it so that you can skip a level with it?

But the area from other levels will be loaded correctly, unlike the area overflow bug right? If the answer is yes, then it would be very great gimmick!
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There is also the unused thing that gets you to the world map right?


All this needs to go in the wiki... (surprise, surprise Hiccup is advertising the wiki again)

Well, now that you say it, it just so happen that byte 10 controls the area, byte 11 the level, byte 12 the world and byte 13 the entrance.
I mean, from a dev's POV it's more convenient to place them next to each other rather than to scatter those settings all over the place (which support your theory that devs indeed coded this on purpose and intended to further develop this feature at one point).

Video Time :
http://www.dailymotion.com/video/x223bsp
Of course it works on both emulators and flashcarts ; this is just an example, hence the broken tilesets on some places.

Thinking about it, I have the gut feeling that there's a way to change to zoom setting of a view without resorting to sprite 84 (kinda like NSMB Wii), has anyone found something yet ?

Matrako also made a boss rush (it took me a few times to beat it, but it could be harder - no powerups).

EDIT:

It uses one of the area overflow things, thus the lack of music (I edited music in to the video).

Actually, Matrako's boss blitz* is the reason I went out of my way to find something that could allow us to backtrack areas from previous worlds, and also the fact that bosses can only be loaded in their respective areas.
Personally I think a boss run is much more fitting for the last level rather than level 1-A (no offense, Matrako).

*yeah "boss blitz", "boss run", "boss rush", they mean all the same but for some reason I find "boss blitz" to have a nice ring going for it.

Although, 1-A is a bonus level, to defend Matrako (who isn't here).