Here's the very first prompt I used when starting my Bitcoin Reef game. I asked it to create the specs before writing the code. I went through 32 iterations. Most of those iterations were messing with the shark design.
prompt: let's make a web app one page game that involves shark teeth and bitcoin. The idea is a player swimming around a 2d screen collecting teeth to convert into bitcoin. we want the sprites to look like shark teeth and bitcoin. write mvp specs for this game.