It's gonna be a long one, but don't worry. I would just like to point out some things I noticed.
I like the idea, but it could need some more tweaking. The movement was problematic. You kept sticking to the walls. to remedy this, you should add a physics 2d material to the player and change its friction coefficient to 0.
I didn't even need the heat gun. I was just able to pour water and freeze it with my gun to create platforms. I wasn't really able to properly use the heat gun. It was slow it lasted for a very short time and reloaded for a while as well. After evaporating ice, the water falling down wasn't all that useful since I didn't have my freeze gun in time.
In terms of the graphics, it looked odd. I think I know, why? Just look at the first screen shot.
Different sprites have different sizes. This means that for example, the background or the water have a different size of a single pixel than let's say, the player. In pixel art, if you use assets that have a different pixel density the game starts looking weird.
Typically you would also have a constant pixel per screen size ratio. So maybe your in-game viewport has a resolution of 640x360. Then for every single pixel of your screen you would have 1 pixel of your game. Then if you viewed your game on a full hd monitor (1920x1080) this would mean that for every 3 pixels of your screen you have a single pixel of your game. In your case, the ground tiles keep stretching and they have different widths. Maybe for every 2.5 pixels of your screen you get a single pixel of your game. What's the screen gonna do with half a pixel? Nothing. That's why people typically aim, for the camera to have 320x180 or 640x360 resolution. They both have 16:9 ratio which is the most common ratio out there.
I saw that you used the pixel perfect camera, but there were some scaling problems, so I just had to say it.
Anyways, good job!