What worked:
I like the switching mechanic. Having two separate worlds that you have to interact with to progress works well. The concept of a rougelite being slower or having more puzzle elements than action is an interesting idea to pursue. The art looks cool, and I like the main character. Being able to choose when to fight the boss at any level (once you have enough resources) is a cool idea, letting the player decide when they want to take a swing at it. I never got stuck in any walls either which is usually a problem in world switching games during jams, so great job there!
What didn't:
The art for the traps is a bit unclear. After running into it, I of course realize it'll kill me, but it's still a bit hard to tell/see at a glance due to how thin it is.
I didn't realize I could interact with barrels and chests at first. Maybe more direction is needed?
I might have missed something, but I never found a way to deal with the bats. I entered the boss arena once before immediately being swarmed with bats. Is there an attack? Maybe after fully upgrading light?
I didn't really see a point to having the world switching based on a timer, aside from no traps being in the light world. There aren't really many benefits to being in either world (aside from some barrels and chests) throughout the main portion of the game, so I would rapidly flick between the two if I needed to smash a barrel or pass a wall. It might be helpful if you want to keep this mechanic to add a reason that the player can only access the light world for small periods of time (timed mechanics, enemies disappear, negate projectiles).
Upgrades feel overpriced. As the game progresses, you tend to either be wandering around smashing barrels, or dying immediately to a bat. In this sense it also feels slow to repeat this over and over to get a small upgrade.
Bugs:
Didn't see any.
Great job!