Re logo: IMHO it should do more than capture the game's shadowy themes, it should capture the specific aesthetic, and the high level of artistry, as well.
A major draw for me initially with this game was the aesthetic, and it'd be helpful to be able to hook people with your logo much the same way you might hook them with a good screenshot. Your logo won't just be on the title screen, but will be plastered all over your marketing, websites, articles, Steam Store, etc: sometimes something so simple can be the deciding factor between someone digging further or moving along to something else.
For example, what about the logo being a mini-level itself? Like the letters being made of blocks like this, maybe even animated to move in and out with a little character traversing them:
Maybe even some little charming touches like the character going in and out of doors, chasing/being chased by shadow monsters, etc.:
If this is done in 3D, it might even be particularly impactful to have a light moving in the scene, showing the dynamic nature of the lighting, such as the overhead light in this screenshot (that's dynamically lit in 3D, right?):
I wouldn't sweat this detail *too* much, but perhaps an easy shortcut is to design it just like you're designing the game itself, and it will naturally capture what's special about the game. And don't underestimate the fact that a good portion of your purchases will come from people casually browsing GOG, Steam, Humble Store, Itch.io, etc and your sole chance at getting your foot in the foor with that buyer will be a logo that speaks to them
Good luck!