Dig Dug: Digging Strike Bonus levels
Get all dinosaur fossils in levels 1 through 12 to unlock the first two bonus islands (13, 14). In those stages are the fossils that will allow you to reach the last level (15).
Hard mode
Successfully complete levels 1 through 12 to unlock the Hard difficulty setting.
Sound Test option
Drown the monster in level 12 to unlock the “Sound Test” option.
The image featured at the top of this post is ©The Legend of Heroes: Trails of Cold Steel III key art / Original