I very much like the core concept, however there are some points in the execution that I feel could be significantly improved. Mainly, the pace. For a game jam, completion takes way too long. I think it took me like half an hour to an hour explore the entire level, with some frustrations along the way. With out your firefly, visibility is almost zero, and with no way to regain it, you might as well reset yourself to the beginning and start the arduous journey again. Additionally, during exploration, you might accidentally die without having used your firefly at all, basically wasting the time spent. I believe if the player automatically dropped a firefly upon death, it could improve the players quality of life. There's no checkpoints throughout the level, and while adding them would lead to faster exploration since you don't need to go through areas you've been in already, adding them, i believe would distract from the main mechanic of lighting the path. I think speeding up the movement would be a better way. Maybe even a dash?
Some other minor things i noticed, the players gravity feels weird? The player character falls very slowly, suggesting a low gravity environment (which i thought at first), except the fireflies flap too quickly for that. With the player character being a kind of mage, i think adding some magic particles could suggest a kind of slowfall spell?
The slow-motion on death feels poorly implemented and more like the frame rate is dropping than an intended feature, and there's a bug where an intense force is applied to the character on death, pushing them quite a distance.
(oh, and the level completion trigger isn't working so I didn't even notice I won the game)
With that out of the way, the level design, while sadistic would have been fun to explore if it wasn't for the issues above. And the player characters art is delightful, and I love the fireflies (though their light could be a bit warmer.