I personally don't really like maze levels, but this one was alright (it had an interesting layout).
Some feedback:
When you start the level you have to fall for some time before you can actually start playing. This can get quite tedious and the start could just be relocated to the bottom.
I don't know what happened to this vine, but I think it's best to change it to a blue colored original vine, or something else.
This is just evil. I strongly suggest you remove this death room.
I believe other people already mentioned the graphics, but they are really inconsistent. You have some good tiles, and the left picture looks good (although you have some tiles for the bottom of the platforms too), but in the right picture there is no snow on top. The level will look nicer and will be more fun to play if you change the graphics to look more like the left screen.
When Mario enters one of these pipes, he will walk in the air for a moment.
This can be solved by placing all the warps on the floor, like in the right screenshot.
This switch does nothing at the moment. I believe it has to active ex-mode, which will just summon a bunch of enemies. But from what I saw in the editor, there will be too much enemies. If you are still implementing ex-mode, maybe decrease the amount of enemies and/or add a extra star (the smw version, so the level won't end) somewhere so it will be worth to press the switch (and also give a hint where it is, if you place it).
There are too many rinkas. Just replace them all with one or two below the mousers.
Your level uses the roullete exit, but it needs to use the smb3 star exit (the same one you used for the secret).
Hope this helps.