Very cool idea, very good execution! I'm unfortunately not smart enough to use the mechanics to their full potential, but this was really well done.
The main gameplay of firing light in a laser then reflecting, diffracting or compressing it to fight enemies is cool as hell, and the objects (densouls iirc?) that you've given us work wonderfully to make it happen. I had no issues with the combat, though I do think the healing was extremely slow compared to the speed and damage of the enemies, I didn't end up using it much. The actual mechanics of the light worked really well, and a concept like this in a jam time frame would definitely be prone to bugs, so I'm quite impressed at how cleanly it functions! I would suggest changing the placement button from CTRL to maybe SHIFT for a web build, I CTRL+W closed the tab a few times lol
Graphics were nice and simple, I liked the enemies and the way you used actual light in the environment. The enemy sprites were good, the player and the beam look sufficiently unusual for it to feel like they're not from the shadows like the monsters are. The beam looked good, though potentially could've done with some more FX, e.g: hitting an enemy, hitting a densoul. The audio was good as well, the beam sounded as strong as it felt and it all seemed pretty consistent! Again, maybe some more FX for hitting the enemies could help juice the game up a little.
I did also notice that the game uses pixel art in some places, and line art in others. It's not a huge deal for a jam game, but it could definitely enhance the visuals a little bit if you made them all the same- the majority of the game is pixel art, so maybe making the text and densoul particles pixel too could tie it all together a little more. I do think that maps with pre-placed densouls could be a cool idea too, so that I'm not limited in power by my own stupidity as much :) Could potentially add some depth and strategy to player placement too if you need to work around what's already there?
Overall liked this quite a bit!! Gameplay concept and execution was really cool and the rest of the game fits it nicely :))