The chapter delves into the methodology of designing platform games like Celeste, emphasizing playtesting and feedback to create fun challenges aligned with the intended experience. It discusses the complexity of the 5000 line long player class in Celeste, tracking constants and conditions for movement, and compares design approaches between Celeste and the upcoming game Earthblade. The conversation also explores technological advancements in game development, improvements in programming practices over the years, and the importance of efficient memory management for high performance.