Unity microgame was created along the Udemy course "How To Create 2D Defender Game With Unity & C#" which I CAN'T recommend to anyone.
Seriously, never buy this course.
The game code is a mix of what was told in the course and what I've learned elsewhere. Unfortunately, the source of the assets is unknown, so I can't give a credit to the author(s) - the assets were provided by the course. Maybe someone finds this repo useful.