Not bad, not bad! Just a few notes before it can be accepted.
- smoke coming out of nowhere looks a bit odd
- floating level title, shadow of a non-existent bridge aren't so great
Why the invisible block?
Very tiny cutoff problems (pipe+blocks, blocks+water). You could make your hack look more professional by fixing these.
Bad camera position for secondary entrance. This diagram
It may be just me, but these castle ground tiles look a bit weird without corner tiles.
Unfinished level or not, the Bullet Bills shouldn't come out of nowhere (use Bullet Machines and Shooters instead). Also, it'd be nicer if you added a side exit so the player won't have to die at the end of the unfinished level.
That's it, good luck!