The nucleus of a lead atom (atomic number 82) is bouncing around the screen. The player controls a crosshair with which they fire loose protons at the nucleus. If the player strikes the nucleus directly, a proton is knocked off of the nucleus, reducing the atomic number by one. However, as atomic number decreases, the nucleus becomes smaller and faster, making it harder to hit. Indirect hits and near-misses increase the atomic number as the loose proton bonds with the nucleus. High atomic numbers produce radiation that threaten the player. If the player can hit the nucleus enough times to reduce the atomic number to that of gold (79), they have successfully transmuted lead into gold!