I will like seeing some new materials conceived of being shown for fantasy worlds, which roleplayers can come across, or be commonly involved with. I do this in my own writing, I mean materials like different metals, or unique gemstones, or various plants being uniquely different. After all, these are worlds that will have different creatures. In my writing I even include different solar gases, with different properties from any we are familiar with in our worlds. Very different materials could have explanation of being from a different world or different realm, or perhaps from meteors that fall somewhere in the general area. Some of my inspiration for this is from Lovecraft. But this approach could be used in any fantasy.