I really like the scene transition, which appears like a mouth chomping down! The music in the title screen is nice, though it does call attention to the fact that there's no music during the levels.

I got to level 5 before this happened, and up to that point the concept of changing only appeared once, when turning into a telephone. Which is a neat idea, except the only purpose of turning into a telephone appears to be that you must then turn back to the usual flower vase to progress to the exit.

Speaking of the exit, as has also been noted by others, there's a problem where the collider(s) do not match up with the visuals. It's entirely possible to do what appears to be a safe landing only to explode immediately. I'm not sure why the sides of the exit are as lethal as the moving obstacles and was very surprised when, at one point, I was able to land on the regular ground with only a bit of damage instead of instant death.

From what I've seen of the first five levels, they're all very similar in design. This could actually be advantageous giving the concept of controlling a shapeshifting object, if only that was leveraged earlier on. For example:

Begin the first level as a flower vase as is the case right now. That's fun and a bit weird and perhaps a little bit of a reference. Then, in the second level, start as a different object like the telephone. (This gives the player the feeling of "Oh, this is different!" instead of "Oh no, not again!") In the third level, start as a larger object (ideally not the same object from either of the first two levels) and shift to a smaller one when encountering a narrow gap. This way, rather than starting as the desired shape and being forced to switch back and forth, you can show off how shape changing is beneficial to the player rather than detrimental.

Structuring the levels this way can give a sense of progression through more complex gameplay, as well as increasing difficulty. Since the game is called Polymorph and the concept is shape changing, introduce that very early and show how it makes your game unique. :)

I enjoyed the game, but a few frustration points kept me from waiting to keep trying.
Mostly the hit boxes not being quite aligned, and the landing was realllyyyy touchy (which might be a good thing). 

Would definitely come back and play an update version :)

Cool idea trying to use different shaped rockets to clear different obstacles, brought me back to the days of playing space flight simulator. Trying to get through the moving walls was a bit frustrating especially the horizontal ones. i cleared four levels before encountering a bug where it seemed after dying to damage, the pop up asking to play again would repeatedly come up when trying to play again, Overall good job!

I was not expecting a mars lander flower vase!  The gameplay was challenging and fun at first.  

There are some things that should be improved that make the game frustrating to play (nit picking).  I think the hitbox of the vase is larger than what the model shows.  I kept dying when it looked like I cleared an obstacle.  Clearances were a bit too tight anyways.  I kept dying when I wasn't moving.  I think the health and player model didn't properly reset after each attempt.

I did get to level 4 where you introduce swapping your model to solve different challenges.  I would play through more of the levels if I wasn't so frustrated.