1. Coal is a bit funky rn due to how the RNG works, but I can buff it so it produces coal more often, I also plan on a charcoal-esque recipe to also help out with these.
2. Save games will be 95% compatible, but like I said during one of the devlogs, saves may break due to changes with RPG Maker plugins, but I will add a proper patching system so these issues will be minimized.
3. There is only one life cube, after all this is a pre-alpha build so the other life cubes will be added as rewards/secrets for later points in the game.
4. Yes! I can change it so can upgrade your variant and element, I just have to edit some parameters but yeah I can make it so that can happen.