An idea I had a while ago that I eventually plan to get back to that was quite fun is a rogue like farming simulator where you gather seeds to make plants and fight demons. You can get a specfic plant that lets you place seeds in a pod that will appear in your next lifetime and enable you to gather new seeds across multiple worlds. You can then make combination plants from your seeds. In order to be able to win you would have to go through multiple worlds gathering seeds.