I'm in the process of fleshing out some ideas for a story and one part of the story centers around a golf ball sized hemispherical hopping toy. I want the toy to be magical in the sense that it is made from a material that is physically impossible in our universe. Whatever this material is I want it to actually be impossible. (with our current understandings) So things like neutron star stuff, black hole stuff, antimatter, quark crystals etc are ruled out because they exist. One idea might be a material that is a gigantic, hoppy-toy shaped superposition, which is stable at all temperatures. Another idea might be frozen quantum foam. I'd be interested in getting some other ideas for impossible materials along with tests we could use to determine that they are not of this world. I'm not looking for elves and hobbits or wizards and sorcerers types of magic, but materials that would be scientifically magical. Any ideas appreciated.