This is not a jam where you make a game. This is a jam where you make everything else.
We're talking instruction booklets, concept art, soundtracks, readme files, strategy guides, character build FAQs; whatever and however far you want to take it, without actually having something playable. After looking through what you've made, people should be only able to play your game in their daydreams.
It's not about rankings or competition or even finishing anything. It's about taking an idea for a game and doing literally everything else regarding it that doesn't involve making the actual game.
OPTIONAL THEME: Excessive! Whether that means art, game mechanics, or whatever you feel works for you!