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The Key is an item in the SNES and PC releases of Mario's Time Machine. It is a spare key to the mayor of Mainz' favorite book, which is valuable enough to warrant a lock. It is given to Mario by a metalworker in Mainz, who demonstrates the quality of his work by freely giving it to Mario. After the librarian mentions that the original key to the mayor's book is missing, Mario gives him the one in his possession. The librarian is overjoyed to have it, and becomes willing to answer Mario's questions about Johann Gutenberg.