Ok, so I played the level, and here are my thoughts.
The level itself was pretty fun. I liked the details you put in, however, a bit of it clashed, like the SMB3 cave blocks and the SMW bushes. On that note, I didn't really understand why some of the bushes were stuck in the roof, as seen here.

I'm guessing they were meant to be foliage growing in the cave roof top, but I feel there would have been better graphics to use to represent this.
I also didn't really understand what those chain-like things in the ground were meant to be.
Overall, it looked quite nice aesthetically, but a bit of clash and confusing placements made it not look as good as it could have been.
However, the NPCs and Mario sprites blended very well, in my opinion.
Next was level design. The first section was pretty simple, with pipes and some gaps being the only real threat.
The next section was probably the most interesting, with the vines that carried you across the level. I like how there was an easy section before the harder one, to help the player get used to the concept. However, I felt it was a little easy anyway, so maybe you could have included falling projectiles from the top or something like that.
Music was good too, but it felt a little lonely and I didn't think it was too fitting for the environment.
My final score is a 6.5/10 or a 7/10. For a first level, it was pretty good, with only a few gripes I had. Well done!