The game has a nice atmosphere, and the music is really cool. I also like the visual design, although I often find that some elements aren't super clear (it took me a hit to realize the lit areas were lit areas for instance)
Now for what didn't work for me :
-after the first death, skully would repeat its "great we're back to start" every time I entered a room
-being hurt by light didn't show the character health decreasing so I had a surprise death to a monster
-right when starting when I jumped at max height the background would be glitched a bit, this went away after I travelled right and left a bit, maybe that was only an issue on my end
-dash can be finicky when it comes on corners but doesn't land on solid ground
About design choices :
-the dash item looks like a flame so when i first came into its room (which taught me to avoid light) I was thinking it would be an enemy, whereas the real enemies were the bland looking mobs left and right.
-the character feels a bit tedious to control (she's basically a truck). With simply moving I can cope, but the jump is very slow when going up and it feels like a drag. During the boss fight I couldn't react to its dash because of the jump, or at least that's how it felt. the character's scream also takes time to do its animation, so when I jump to hit something often the scream will start when I'm on the floor... but during the boss fight it still seemed to hit the boss, so that might be a visual issue only.
-I didn't really understand the boss' patterns from its visuals, and the constant screen shake from the scream was adding to the confusion (I also don't know how I managed to beat it).
Finally, it does feel a bit silly that the character is all ghost-like and floaty but affected by gravity. Maybe you could add ghost legs to her sprite or something, or just have the skull say he's heavy or anything like that.
Hope all this helps and doesn't come across too harsh, and I look forward to the development of this game!