It's okay if we've been working on a design document or something though right? I saw the rules said we were encouraged to "have an idea" and I've been making lists of features I need to code once it starts. Is that within the rules?
You CAN use external libraries, game engines, pre-existing code/algorithms, pre-existing art, etc. You can even start your game from an existing game, if you are planning to turn it into something unique. If in doubt, be clear what resources were reused.
If I want to make a roguelike platformer, and I coded a non-roguelike platformer before.
Yes, anything for inspiration and concept is good. Just think if you are working in actual Assets that will be included in the game, these are meant to be done within the challenge timeframe.
