Thanks for checking it out! Much appreciated.
The circular animation is the dissolve ability cooldown. In the published demo it has no much effect. However I'm prototyping additional types of enemies that can have hitpoints. You need to attack them several times, each time stripping one hitpoint. So there is a cooldown period before you can attack again. During that period, the sun may shift a bit and you need to reconsider your aim for the next hit. After a hit, those enemies may also back a bit or teleport to completely different spot in the room. It's a way to scale enemy difficulty within main mechanics constraints.
I may add smaller enemies as well, that are harder to spot but are not lethal. They just inflict some damage on you when the room is shut.
I'm testing boss remnants as well. They are not confined to a room but follow you around in real time and actually hurt you when close. The dissolve cooldown is a tactical consideration when going against them as well.
The last prototype has a key/lock system for doors and possibly windows. Some of them may initially be locked by spells and are unlocked with different "keys" obtained when killing specific remnants.
Regarding light reaching remnants: The remnant position within the room is currently completely random. I've implemented a check if a spot is reachable by light, but it's not yet applied to enemies. The light is always quite low and current remnants are rather big/tall. I've not yet encountered a situation that a remnants is not reachable. Even if it's positioned in a long corridor far from a single window, there are always doors to open and let the light from adjacent rooms do the job.
Yeah the general idea is to have a string of levels with increasing size/difficulty and maybe some bits of narrative that link them together.