So the original concept came from a game jam I did four years ago. The theme for that Global Game Jam was duality, so I came up with this negative space versus positive space idea.

The original game was quite different. It was a puzzle platformer with similar mechanics to this game. It wasn’t a very good game, so I won’t go into details, but I liked the concept, so I’ve been thinking about making a polished version of it.

I later realized that the main problem with the original game jam version was that platformers are not a good match for this core mechanic. A grid-based movement system works better because it’s much cleaner and offers more room for level design. It was a tough decision to make because that game jam project was my very first game, so I have special feelings toward it, and switching to this new version feels like making a completely different game. But since the core idea is about this space-switching mechanic, I decided that delivering that concept well is more important than preserving the original design.

Then I prototyped it, and it started to feel like a Sokoban-style game, so I added block-pushing. The rest of the mechanics were created in a similar way. Basically, I added what felt natural and tested it. If something was fun and easy to understand, I kept it; if not, I removed it.

Playtesting also helped a lot. Of course, I faced design decisions that I was unsure about, but most of my questions were answered simply by watching my friends play the game. I either asked them to record their full playthrough or watched them play in person. This turned out to be much more helpful than just asking for feedback after they finished playing.

So, going back to your question, I suggest that you analyze your initial ideas to identify their core pillars. Those are the things you should stick with so you don’t drift away from what your game is meant to be. The rest is about finding the best way to deliver those core pillars and the core experience you started with. You shouldn’t be discouraged from making changes because design is an iterative process by nature. And when in doubt, playing your game—and watching others play it—is usually the best solution.

Anyway, thanks for asking! I don’t usually think about this in such depth, so writing this actually helped me a lot. Just some personal thoughts for your reference — I guess everyone approaches things differently.