1. Either the lava is too high or the ground is too low.
2. The BG doesn't look like its for volcano's. It looks like its for normal snow places.
3. Why not try to make the slope more interesting. Straight lines aren't that good.
4. Where did the snow ball come from.
5. In 0:26 of the video, the blocks should be one space higher.
6. In 0:35 of the video, there is a tileset cutoff.
7. Speaking of that timeframe, the lava is a bit too high.
8. & the coins are a bit too low.
9. In 0:58, The pipe is way too close to the end of the screen.
10. There is a looping error in the sound at 1:05
11. in 1:15, there is another tileset cutoff. One on the left platform on the right.
12. Another one on the right platform on the left
13. There is another one of the right platform on the bottom right.
14. in 2:05, the coins mario are on is waay too low.
15. In 2:23, you should make the platform from be on layer two, with you being able to walk on it, like semi solids from SMM.

Overall, this is one of your more creative levels and I like that. Keep it up.

I think you should try to make a custom BG. For example, change the colors to be more red toned.