I really like how the number 666 is implemented here, and how shooting clones a bullet instead of a raycast. Wish more games did that.
The idea of being able to teleport through some invisible portals similar to how the demons do is quite cool as well, however, I ran into an issue where I managed to shoot a demon a couple of times, it then disappeared after crossing a portal... And I was stuck waiting there for another demon to spawn, but it never did. May have been a bug I triggered without knowing, or maybe I'm just impatient and the reward comes after the timer ends, but still quite an annoying thing to run into.
But anyway, I enjoyed this game but found the "aim then shoot" mechanic to be quite pointless, maybe aiming could increase precision at the cost of a slower fire rate or make your bullets faster... Or just be generic and zoom in to let the player see where they're aiming better.