ABOUT SHADOWING

If you think that the Secret Worlds are definitely something different or new, you've got another think coming! Every single pixel of the secret worlds are just screwed up versions of actual areas of the game. So to be perfectly honest, I can't say that you're actually in a totally new area, just scrambled regular sections.

Since the paragraph above probably made absolutely no sense to you, I've made an example which should make this more clear:
Included files:
SHADEX.GIF
SHASHIP.GIF
SHASHIP2.GIF

See? You're nowhere new, but you're not in the same place either. Also, things shared between SW1 and SW2 can also be different! (For example, the two ships.)

But, there is a more technical explanation to shadowing too...
Every normal area of the game (they fade in between) is composed of different styles of blocks and tiles. The areas are put together as a code, which is what's saved on the cartridge. In this code are different atributes which call for the different tiles, and where to put them. Some tiles are blocks, some are acid, some spikes, and others are acid.
Only one set of tiles can be loaded into the Gameboy at one time, and when you enter a different area (the screen fades to black and fades back in), it's actually using the time to load up a new set of tile patterns with the slightly different codes, and at times, new music (which is not important in this case). If the same set is kept while Samus enters a different area, it will look badly scrambled about 90 percent of the time. Wall blocks can instead be background tiles, and sometimes the backgrounds turn into walls! But, you'll never enter a different area without the fade... or will you?
Secret Worlds are actually the code of a different area which is still calling for tiles in the area from which you entered the secret world! Because of this, everything looks screwed up when the right blocks are put together by the the wrong code. Cool, huh?

(http://m2sw.zophar.net)