Like for many of you it was the first jam for me as well.
At the beginning I was very nervous, I had no idea what to make and I worked in solo, so I don't have anybody to rely on their ideas either.
Then I was thinking about a negative battle royal (where the goal is to die as soon as possible, and the last one standing is the looser). Then I realized, I have no idea how to do multiplayer... and I work alone... and I only have two days... so I passed the idea... :D
Then I started doodling in Godot, made a few prototypes. A basic top down shooter was born. Ok, that's a good start. Now I need to make it to fit the theme. My first idea was to use a bow and arrow, and you would always have to pick up the arrow after you shoot. It was interesting, but I didn't quite like it.
After this I changed the concept of moving to follow the mouse (before that it was a classic WASD move system). Now the game only used one button for shooting, and the player always followed the cursor. That's when it started to get interesting. I thought, what if I can alternate between moving and shooting with the same button? Press for shoot, hold for move (and swipe for change weapons, - I cut this part out from the final game, but it will be back in a future release), so I changed the bow to a gun and my game was born.
After this I made a small dungeon (at this point there was only few hours left from the jam) added zombies, keys and doors, almost broke the whole game, added doors and keys again. And then the lights. I never used the lights in Godot before, so I have no idea how they work, but I really needed them for the atmosphere, so I jumped into the docs and read through all of them. I still used a lot of hacks because I was to lazy to implement them in the 'right' way (or just had no idea how else could I do...), but in the end it somehow became a whole. :)
Long story short I had a lot of fun, and learned a lot, and from the few responses I got until now I feel, that it worth it. Thank you! :)
Here is my game: https://itch.io/jam/gmtk-2019/rate/462640