OMG A NOO MAWD!!! =D It's been so long since I've seen one, I was beginning to forget what they look like...
New music is very nice. I actually kinda like the death music, just because it makes me laugh, and this is kind of a lulzy mod anyway.
The first secret isn't really much of a secret. I would recommend making it a bit less obvious; maybe instead of a door (which just begs to be entered) make it some other landmark which would make some player curious enough to try interacting with it, but could be dismissed as decoration. The second one was a bit more secretive. Any others were either nonexistent or well hidden, because I didn't find them. I think it would be better if the secrets were in ascending order of rewardingness (i.e. you find weaker weapons first, as opposed to now where you find the snake first, then the fireball).
I would recommend being consistent with the type of savepoints you use. Sometimes you just have a v-trigger, and sometimes a disk on the ground; it gives the mod more unity if you stick to one or the other.
Gameplay throughout the mod so far is generally good and entertaining.
Careful about exposed slopes; the Cave Story engine has a glitch where it bumps you up on top of a slope if you touch the side of it. Solution: make sure the sides of slopes aren't exposed.
Be sure that any time you use a <FOM with a number other than 16, you use <FOM0016 before you get to the <END. Otherwise, the camera will continue to track the player's movements either too slow or too fast. In your mod, there are several places where the camera's motion is too fast, and it's really distracting.
The area with the bed, gaudis, and computer is neat in terms of the slight non-linearity it adds. After beating Pooh Black, however, you might want to make some clear indicator of where you need to "interact" (press down), so people (DT) don't think they've gotten stuck and/or reached the end of the demo.
Oh nice, a puzzle/maze thingy, I likes. My only suggestion here is that you use <FON or <FOM (whichever one you use when you go through a door) with a number greater than 1, so the player can visually follow the camera as it moves from one door to the next. If you don't like the way the camera slows down as it approaches its target, you can do something like this:
which will make the camera move at a constant speed toward the target. In the above example, the movement would take 10 frames (1/5 of a second, if the game is running optimally). This may be a bit short, so if you did that, you might want to increase the number of frames. If you don't mind the way the camera moves by default, then don't worry about all that.
The blade makes the 2nd and 3rd boss fights painfully easy...
Well this is odd; not sure if it was intentional. In the ice area, there's one spot where I enter an apparently deserted one tile wide path, and behold, I am surrounded by a multitude of the Heavenly Host, praising God and singing, "BOINGYBOINGYBOINGY!". A few shots of the snake reveal that several critters are bouncing unseen in apparently solid tiles, unable to escape.
Anyway, good job and I eagerly await the next demo!