Fox developed almost the whole game by himself. He wrote the words and made the music by himself, and only used a few pieces of extra art given to him by other artists. The game was inspired by the "Mother" and "Mario & Luigi" role-playing series, the "bullet hell" shooter series "Touhou Project", and the British comedy show "Mr. Bean". "Undertale" was originally meant to be two hours long and released in mid-2014, but creating the game took over three years, making the story longer and not making the game available until much later.