If you want you could try to add more upgrades and more content into hell and when you get into hell you can have a new set of upgrades while keeping your previous ones and when you get to a certain part there can be a portal that takes you to like an alternate reality or the surface of a new planet and you can get like new resources and you can make up your own or use a different set of resources from the periodic table that sound "other worldly". Just an Idea. Hope you use it. Thanks.