Cause so many users asked this I decided to make tutorial here.

Information:

With this method you can edit all the textures of Mario and Luigi.
You also can edit their models. I will not show that here, but if you want to do it,
then note that you can only edit their head models!

You will need:
-The New Super Mario Bros. Editor (NSMBe)
-A New Super Mario Bros. ROM
-A copy of your ROM


Take NSMBe and open the first ROM.











Now you should open another ROM with NSMBe because of the edited .nsbtx file.
Go to the Filebrowser and open the same path as in the beginning of this tutorial.





Aaaaaaaaand it's done
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

Import it into another Slot than the desert slot.
Then it should work!
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

There's one (kind of) good thing about using this let-an-entrance-for-example-a-pipe-get-ya-out-of-the-level-feature :
The level won't be signed as finished and the star coins not as collected that's true...
but you even can't continue ever to world 2 so it stays a real 1 world hack if you know what I mean

_{P.S: Your post must have come from hell...}
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

You mean *...to go from Area 1 to Area 2 but...* ?!

Maybe one of your settings is wrong?!
Your Pipe Entrance in Area 1 has to be like that:

-Entrance ID = (Choose one)
-Camera X = (Depends on where the Entrance is, but normally leave 0)
-Camera Y = (Depends on where the Entrance is, but normally leave 0)
-Destination Area = 2
-Destination ID = (Entrance ID of your Entrance in Area 2 where you should come out from the pipe)
-Connected Pipe ID = (Only for Connected-Camera-Followed-Pipes, you dont need it, leave 0)
-View = (Number of the view the Entrance is in)

If it doesnt works or something else simply make Screenshots of your entrance settings / upload your Level / upload the patch so we can have a look on it
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

So it has not to be a single level (.nml) and can also be a patch of one level (.nmp) ?
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

Okay, I made one !
It's a bit hard and not that good but yeah
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

Next time use the search funktion
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

If you really want to do it like on the picture you can do that:
(Im sure you dont want the player to see the room until he doesnt falls down, right?!)
So I expanded the tiles in the view 3 blocks to the bottom.
You then have to expand the view to the y level where the ground of your secret room is.
Tick scroll vertically in the view settings.
After that you place the sprites "In air vertical scroll stop right/left" on the y axis where you expanded the tiles before.
IIRC Dirbaio has explained the workings of those camera sprites somewhere... Im sure you'll find it with the search function!
The only place where the scrolling should not be stopped is the hole so let free space there. Do the same camera thing on the other side.
The reason why expanding the tiles to 3 is cause if you dont do it you have to set the scroll stop on the y axis of the ground and if you then jump over a hole there will be a camera bug (that is not relevant in 2-1 because there you dont jump over a hole, you can only enter it!).
I also set another Camera Sprite at the beginning of the level that avoids a camera bug at level start. And I placed some horizontal scroll stoppers in the secret room so that you cannot see the missing ground tiles.I also used tileset 1 instead of brick blocks from tileset 0.
...okay that would sound a bit hard to understand so just look how I made it

Downlaod: http://nsmbhd.net/get.php?id=3884

And watch out! What you placed in the room arent coins...

Anyway, welcome to NSMBHD

_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

Here's my!
I havent used a shadow on the picture cause I find it better this way.
Anyway it doesnt looks that good, I have to learn image editing
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

Go to ROM File Browser root\player There you have to decompress whatever file you want to edit and export it. Then import it into a .nsbtx for example b_lift.nsbtx in the enemy folder and open it. Then you can edit it there! Now export it and import it into the Mario file again and compress it.


_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

The Overlay that has to be decompressed is Overlay 9_8
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

Isn't a model always 3D?^^
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

It's a shame that it doesnt work and...
um, not that much I think.

Because you can just do this "entrance thing" like in the Mushroom Background Chooser house to exit a level using an entrance (f. e. a door) without dying or reaching the flagpole. Well, it does kinda the same thing as Toadsworth "should" do. Of course you've got any time you wish in the level.

So why trying a harder way instead of an easier that does the same?!

_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

Just to clear what I mean:
What I did is comparing header block 6 from a Mushroom House with block 6 of a normal level.
I don't remember correctly what byte(s) exactly to change, (copying the whole block should do it too.)
And then every entrance you enter in this level sends you to the world map. (not sure if the warp sprite works)
Just like in the mushroom house, so the level is not finished when leaving it. That's the problem!

edit: the warp sprite works as always

edit2: I forgot to say that I downloaded your level and tried this toadsworth thing out by myself. The truth is that the unused feature does not really warps you to the world map when you touch the sprite. It just looks like this because the time you need to go to him is kinda the time he warps you automatically to the world map. So if skawo would remove that time limit the sprite would not does sonething anymore - it is useless!
But it could maybe be kind of useful for a speedrun level if you extend the time until the warp.



_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

oh, I never thought of this
Seems really legit what you say. Toadsworth normally ends houses with items and 1-ups (unused nybble too?!) / exit entrances end houses with a door (background changer)
So you think if you would knew how to do that, it could be that the (/some) toad houses won't work anymore because they're not coded as normal levels that can be beaten or not?! Or maybe some other things happen in the houses then...
Something like that could probably happen, but I just tested a flagpole in a toad house. A flagpole normally finish a level but in the toad houses everything worked too. So a entrance/toadsworth that finishes normal levels will maybe still work in toad houses...
If not there's still the method to use a flagpole in every house, so that the other things aren't used anymore there.

EDIT:

Btw, I just found out, what to do exactly to use the exit entrances in levels

Simply open your level with NSMBe's Hex Editor and go to header block 6. Replace the 20th byte that says 00 with FF, and you're done
Now every entrance you enter will take you to the world map!

Some other information:

-an exit entrance will NOT work if the destination entrance in the entrance's settings is greater than 0 !
-warps will still work as usual

EDIT 2:

hehe, let's change the 00 not to FF, but to another value...
You can change to which level on the world map you will be warped to.
For example 01 warps you to the starting point, 02 to the first level...
Warping to the unused World 6 Cannon is also possible.
If you use some other values like for example AA and then press left 2 times this will happen o.O


There are some quite funny results,but...
This gives us the ability to make for example warp zones that lead to specific levels in a world

Sure, you can warp you to the next level after the one you played, but the level you warped from won't still be marked as finished. So finishing a level with this way is not possible.
Therefore other Hex Editing or ASM is required...

_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...

Well toadsworth is 3D. That means he has a 3D model with textures. In DS games models are .nsbmd files with the textures in it (but sometimes the textures are stored in a .nsbtx)
Files are often named in japanese. So an easy way is to go here and you'll find it quickly!
It's name is Kinoji, so this is probably what you look for in the game's files.

Open NSMBe, go to the ROM File Browser Tab and navigate to the enemy folder. This is the folder where the most 3D models are.
Look for the file and make sure whether it's a .nsbtx or a .nsbmd file and open it with a double click.
Here you see the textures of the model. Click "Export this bitmap" and edit it in a external image editing program the way you want. Finally just click "Import this bitmap with a recreate palette" and choose your edited image.

Done
_________________________
I'm out of Hacking. Of ALL HACKING...
I don't know how long, but there are so many reasons why I have no time to be here for a (long) while or to hack some game
sry guys...