Ok, I downloaded the demo and here is my feedback:
The lua stuff impressed me. Maybe the controls for the wall jump were too hard in the beginning but it's ok.
Now the problems are that you put exit stars as hidden stars. So if you get a hidden star and play the level again, you can't get the normal exit star.
Some levels were a little bit difficult for the first world, but it makes up for that cuz of that big Mario when getting hit with a powerup.
World 1 map:
I find the graphics ok with some decorations. Sunken castle graphic was nice. Some paths are long but it's not that noticeable.
Level names were barely noticeable cuz of the background picture.
Some graphics were confusing like the castle which I thought was a platform. It costed me a life.
The 1-up was easy to get.
Meh never really played it after getting that star from air bubbles at the beginning of the level.
Probably the best level but has a bug.
First thing I would like to mention was the saw hitbox was misleading. It is much smaller than the actual graphic.
The switch puzzles were painful if you died on the red switch one so it makes you go back and redo the entire level.
Especially with those fire bars.
If you get a fire flower you can kill the enemy and it drops a coin.
But if you shoot it at an enemy you can't kill, it keeps giving you coins. That way, you can farm 1-ups.
This works on Skull fishes, bullet bills and Bowser jr.
Bowser jr. boss battle:
Some phases were easy while some were not. Interesting fight and quite fun.
First phase was easy since you just have to shoot the enemies get the bomb and repeat.
Can get hard if you manage to lose your fire flower.
Maaaybe it can get broken if you bring the ice flower from the beginning of the level so you can freeze the enemies and throw them instead of bombs.
This time Bowser jr. stops flying and his clown car turns into a ground vehicle.
This phase is very hard if you lose your powerups.
Probably because Bowser jr. unpredictably moves when colliding with another enemy.
Can get messy if you don't kill the first wave of enemies before the second one spawns.
The fight transfers into a water section and Bowser jr. is more under the dark star's control.
This section was kinda easy but very hard when I played it the first time.
Because I was swimming on the right side of the screen and the dark star "rinkas" and bullet bulls were hard to dodge.
But if you stay in the middle, right after the wave of skulls, it's kinda easy.
After ending the section and jumping into the portal which sends you to the island, my game crashed and I was unable to continue.
I really liked the demo and am looking after the full release!