Has Minor Errors
The main problem I had with this level is that the parabeetles are out of control. They move way too fast and there's no way to get past them without getting hit. The parabeetles also caused a runtime 9 error in the second line guide part. I don't know if any other people had this problem (I don't think they had, judging from the previous posts), but it can be solved by deleting the speed=0.85 in NPC-36's text file. I tested the rest of the level with this problem fixed.
EDIT: This problem might have been caused because my decimal symbol was a comma instead of a dot. I think SMBX thought the speed was 85 instead of 0.85.
In the picture below, there are two parabeetles in the red circle.
When the player slides down the hill, they end up getting hurt because of the lower parabeetle. The upper parabeetle is trapped between the brick and the wall.
You might consider deleting both.
The area in the picture below feels rather empty. I would place a few enemies here.
The midpoint feels a bit lopsided.
Also, the first line guide part over the water is unnecessary, I recommend deleting it and just add a pipe directly to the underground part (the midpoint might be less lopsided if you delete this part).
A small instance of cut-off:
You forgot to lock the door to the castle. Now anyone can go in, even without a key. To solve this, select warp 3 and enable the option locked.
Otherwise, the level plays fine. Keep it up!