I taught myself how to code in 2011 and made an iPhone app that earned several thousand dollars before going to school for game development, which I had to drop out of due to getting really sick. It took over 10 years to recover to the point where I was able to start producing consistent work. Along the years I have done about one or two game jams a year.
Some of the more interesting systems I have built were: A swinging mechanic done mathematically to wrap around corners realistically, a plant growth cycle that did multiple variations on how the plants would "grow" over time with different sprites for different cycles, a monologue system that I was able to use for dialogues without editing the code, and an auto-battle system that travels along a grid with each cell being a battle and as the character progresses through the grid the enemies get stronger and each subsequent grid is stronger than the last one.