Leviatron, while short and feeling more like a demo than a game, makes up for this lack of length with a lovely amount of polish and attention to detail. At first I was confused of why the bones and player seemed so small, however, when the main boss was shown, it became clear why. The difference in scale between the player and boss felt daunting, and really showed a challenge. Matching this scale, the player felt quite powerless, and was easily 'killed' in one shot by anything, but that is made up for by the power introduced. Furthermore, the immediate contrast between the first and second area is noticeable, and makes the boss seem like alot more of a challenge. With the first area being brighter and having easily defeatable enemies the size of the player, then the sudden shift to a much darker area, with bleaker colors and the addition of a heartbeat and lightning[which was clearly made by your mouth by the way :P], really does make the challenge so much more daunting. Not only this but the music, which is must more happier in the first area and gives a calming vibe, shifts in pitch and loudness in the second area once again re-inforcing this eerie and daunting atmosphere.
There is so much to say about this game and its excellence in design, the way it envokes emotions into it's player. In my opinion it really does mark a sign of progression since your last Entry, color jump. And shows how you have developed as a game developer.
There is little negative I can write about this game, its only issue being a bug in which you can get stuck in an infinite death loop, as seen in the following gif: <https://dl.dropboxusercontent.com/s/6kgn4apw4fjo8ho/BOnB2rpXHK.mp4>
However, this can easily be fixed by pressing the R button, and is difficult to achieve, meaning most normal players will easily avoid this.
There is much more I'd like to write, but I seem to be nearing the character limit, so on a final note, I congratulate you Yosi on this game, and am excited to see what you make in future.