Welcome to your first jam, and great job finishing! You've got a good concept going, and I can see you do scale your pixel art well, so we can see those crisp pixels on the trees and fences, though it looks like the cannons and the base (possibly the player and enemies as well) need that treatment as well. You also did a great job with getting those trees shaded well. Here's the nitty gritty for improving this game or for next year's jam:

• Looks like you've got more than four colors in there. I'm counting five shades on the trees.
• As others mentioned in the comments, mouse controls are not valid Game Boy controls :)
• Your game resolution is much larger than the Game Boy's 160 x 144 screen. Keep in mind for the future when you stick to that resolution that when using engines like Unity, you also have to be mindful that things that move in the game adhere to that resolution as well (i.e. no sub-pixel movement or rotation). I'm not sure how it works in Unity, but I'm sure there's some viewport and scaling settings for the project that can set that straight easily.
• I can see from some fence placements and how the player character interacts with the base that the draw order needs some help. The key here is ordering by the Y-position of a sprite; use the bottom of your sprites as the origin point, and a sprite whose Y coordinate is below another sprite should be drawn on top, and vice versa.

Hope to see you again next year!!!

my first ever game jam movements - wasd

inventory - tab

craft menu - b

gather resources - e

rotate fence - q