Nice game. Nice music, nice mechanics. I like it.
A few points of subtle critique from my side:
1) The sound for player and enemy movement was a bit annoying. Maybe lowering the volume or removing it entirely would be better
2) I think it would make it better if the player could get medallion back at any time. There were moments when I would accidentally send medallion into a wrong place and would be forced to blink into my death.
3) idk if it was you who actively disabled fullscreen mode, but accidentally clicking outside the game window was quite annoying.
4) mb for the background (which is nicely done) it would be better to change cell size from 16px to 14px to get rid of all those gaps between squares.
5) I think physics can be slightly improved - if you stay still and blink to your medallion in the mid-air, you would instantly start falling due to gravity, which is correct, but doesn't feel right. Maybe adding part of the speed of the medallion to the player speed right after teleport would make it feel better.