What a unique concept, at first sight i thought it was just a platformer with a single sprite but i was delightfully wrong. The mechanic of adding and substracting parts and them interacting with your total mass for different jump heights is filled with possibilities and requiring a specific shape for the end makes level design managable. 

My only grope with this game would be aesthetics, get some cool style and oh god please throw that chromatic aberration shader to the river and have a viking funeral for it.

Theme,  the only one sprite is cliche and detrimental but being "one with the world" is what really sells the adherence to the theme.

Originality, in spades, a great original concept in a sea of 2D platformers, a breath of fresh air.

The final part of the level was very smart, I really liked it. Only thing that bothered me a bit was the sound when you fail, overall good game, congrats

This game is really original and perfectly fits the theme, but in practice, it feels really tedious, mostly due to the number of inputs to add or remove blocks to progress through the level.
The purpose is a bit defeated when you also understand that you can take the right amount of block to the end, then build your shape there.
I think your game would have greatly benefited from a more "puzzle-oriented" level design, maybe with blocks you can and cannot grab, in a more closed space.

Overall, great idea, but would be better fitted for a different context.