Taiko no Tatsujin 12 Don~! to Zoryoban Arcade Machine, otherwise known as Taiko no Tatsujin 12.5, was released in July 2009 and is an expanded version of 12 - hence the name 'Zoryoban'.
This expansion version includes a whopping 145 songs on debut and 155 after all the secret codes were revealed. There are a total of 11 secret songs and 12 Ura (1 pl) songs, and includes the following genres: J-Pop, Anime, Variety, Children/Folk, Classic, Game Songs and Namco Originals.
Taiko no Tatsujin 12 Don~! to Zoryoban introduced far better songs than 12 and included the 12 Asia exclusive secret songs (the first time these songs had been put in a Japanese machine), and was joined by four to five new Namco Originals! This was also Hatsune Miku's first ever Taiko debut with 'Melt' and 9mm Parabellum Bullet's 'Punishment'.
12.5 introduced Ryougen no Mai, a song so tough it's put up together with some of the hardest songs in history. It also introduced more Ura Oni difficulties than any other arcade too, and crazy ones at that. Even the easiest children song, Mori no Kuma-san, got a very difficult Ura Oni level.
There weren't many, if any, game play changes, that largely stays the same through the 11 and 12 entries.