Each time I start a game project, for game jam or outside of it, I learn that it's best to cut off most features that you get an idea for. Also, it's really not the best idea for game jams to start making a game thinking you'll make a huge RPG. XD Trying to keep things simple and fun is a skill on its own. I've yet to master that.
Anyway, what I learned during this jam was how to make a crude lighting/shadow system with just a couple lines of code. Very simplistic and works well enough for me.
You may see the lighting system in action here: https://itch.io/jam/gamemaker-20/rate/520409