Hi. I've seen this thread and thought I'd take a look on your demo. Then I decided I'd review it.
I got to tell you, your hack needs a bunch of improvement, especially on the level design area. I'm going to post some in-game screenshoots as I get into details.
First things first, the layer 3 on the title screen is a bit too much. When I open the menu some tiles get overflown by it.
When in enter the first level...
Aw, come on, this is the first level, and the first image I have is of a sumo brother throwing fire bolts, a bunch of brick blocks and a pokey which will trap me there if I don't go quick. That's completely unfitting for the situation. The first level should be soft, and the first screen of a level shouldn't be too much overflown like so. Leave the challenges for the rest of the level.
Another issue there: consistency. If I ask you what this level is about, what would you tell me? It has a big variety of enemies, items, level organizations, but it doesn't have a solid gimmick. Everything was put on the level in a sort of random way.
What I recommend is, before you start working on a level, think on what it's going to be about. If you'll base it on an enemy or some sort of ASM hack. Then develop that gimmick gradually as the level goes.
Well, let's go forward.
This area has an incredibly big amount of enemies. If they all showed it would probably be impossible to dodge them. But overflowing a screen with enemies causes slowdown and also causes them to disappear.
If I hit this block from the side, this is my bounce block.
I do not recommend the use of that turning block tile. It... Makes no sense to be there at all. Because a tile exists it doesn't mean you need to use it, y'know.
Yoshi coin in a screen boundary. This happened a lot in your hack. Press F2 and make sure none of them are on the boundary of the horizontal green line, otherwise they can bug pretty easily (they will either cutoff like that or farm you a lot of 1-ups).
Think of the player with yoshi when you design your levels. Speaking of design, this level is just too, well, lazily made (no offense). It's way too short and rather pointless. Why don't you replace it with something different and also bigger?
Little niptick, it doesn't look very good when something blocks your way after you get the goal.
1. This level makes use of the ghost house sprite tileset and lets you access it with yoshi. Not a good combo: use a no yoshi entrance;
2. Just like in the first level (fourth picture), this level has sprite memory issues due to the overflow of sprites. The goal post refuses to show.
Those big spikes affect the way of the line-guided sprites for some reason (also you know they don't work unless they're on layer 2 and controlled by a smasher generator, right?).
Always end your level's contents in the end of a screen, otherwise this will happen.
The events cause some errors in the map. That shell thing beside the door is cutted by its half, and the level I'm standing on doesn't reveal its circle.
Not everyone knows, but the death blocks available on the section will kill you even if you're star Mario (I was actually going to make a version that fixes that stuff). Having a star there can be pretty confusing for the players. You can put a message there telling the muncher will be still harmful.
Yoshi and podoboo don't fit.
Those corners look... Wrong. Also, this chainsaw simply ignores the bottom tile. Don't know why (those line guides are rather annoying anyway).
Those shooters will never shoot anything without the bullet bill shooter sprite. It's sprite C9 (found in the "Special Commands and Generators" field on the add sprites window).
When designing a level with layer 2, always time the positions of the layer 2 when necessary. Everytime I reach this spot, the layer 2 is low, and it made me first think the only way of going through that part was flying. Also, sprite placement on layer 2 can be tricky too: that chuck will simply die on lava if I reach that part while the layer 2 is low.
I stopped in the ghost house, on which I wasn't able to enter. I assume that's the end of the demo.
Most of those are minor bugs, but what I really want to put emphasis to is to what I said about level design on about the beginning of the review. Many of your levels are too much randomly designed; if you base each level in a different idea, then your hack will feel much more organized, professional, and interesting. You can trust me.
It's been a while I don't review a hack with images and stuff, this takes a lot of time and effort, so I hope you will take at least a part of what I pointed out in consideration. And to finish, I wish your good luck with your project! :