A fantastic looking puzzle/platformer with some of the most well thought out and cool mechanics I've seen!
Firstly let me just point out that I almost immediately found a cheese in that you can jump as you are rising on the weighted blocks and it sends you SUPER HIGH. This isn't much of an issue until you get to the 2nd last level where you can just skip most of the level and go straight to the door.
The game looks great, the pixel art is 10/10 and the design of the character, props and environment items are all extremely easy to read and communicate the intent and goal very well. I was a little confused then I first started the game as I changed to gold and couldn't jump past the first little tutorial message. Once I realised changing has an effect on the characters movement though it was quickly resolved without further issues.
The audio is great across the board, very chiptune/retro with some crunchy SFX in there.
The puzzles were a lot of fun too, not to difficult either and had a really steady and well planned increase to the mechanic complexity. Besides the aforementioned cheese there weren't any mechanical issues. I did find the return to the original "charge point?" particularly hard on level 5 though, the first gold/spring trap seems to move much faster than the one later in the level and I died quite a few times.
I really enjoyed the changing metallic properties of the character it would be awesome to see it expanded in the future if you decide to develop the game further or add more levels. I had a lot of fun with this.