This is a very elegant & clever little game! Luring the snake into easier targets is a very good twist. Has the potential to be very addictive, although I was able to put it down when I found the ‘victory’ condition. (I was just trying to surround myself with boxes to see if the snake would leave me alone for a while.)
The ability to move diagonally is a bit too strong (and could serve as the full movement upgrade in itself). I was initially playing without it and once I discovered diagonal movement, it kind of trivialized the difficulty.
I did find the menu a bit confusing at first. I don’t think it was mentioned that the E key was used to confirm. Then I wasn’t sure what I was looking at, and kept hitting play without buying that first movement upgrade, so I kept dying and didn’t really realize why the movement controls weren’t working. I only figured it out after dying 4-5 times.
But yeah, excellent submission! Good sound too.