It's a decent jump 'n' run, but things got weird when I got to the ladybug. First of all the second part of the dialogue got immediately shown before I had a chance to read the first part. After that whenever I fell downward I was blind since the level was replaced by some grey stuff, probably not intentional? Here's a screenshot in case you don't know what I am talking about:https://www.newgrounds.com/dump/item/207a19d21f9d8340237e72824e0564f9

It looks pretty great (the lighting effects really work well). I like the bullet reflection mechanic, as it gives you an incentive to not just spam shots all the time. I cannot figure out what planting shrooms is supposed to do (other than slightly draining your life). The effect of dashing feels pretty weak. Right now the game feels pretty difficult, it's mainly the spreadshot enemies that give me a lot of trouble, I have only made it to the second floor so far because of them.

First of all I think you are off to a good start. I think you could turn this game into a fun shooter. The movement and shooting controls feel natural.
What I don't like is how quickly you run out of health by time just passing. I understand that you want the game to be fast paced, but the way it is now it feels frustrating for me. Combined with the life steal mechanic it took some time for me to figure out how the game even works because I died so quickly.
Dodging the individual enemy attacks feels almost impossible, I just randomly circle around them in the hopes of avoiding getting hit. This combined with the enemies all looking the same (I cannot distinguish their weapons in such a fast paced game) gives me the feeling I cannot really do much more than killing them as quick as possible without much tactics - and randomly insta die due to a shotgun blast sometimes.
The weapons feel a bit unbalanced, the uzi feels far superior to the other weapons while the song/dance item feels useless. Maybe you could turn the song into an insta kill all enemys effect that is independend from your current weapon?