Boss Mode:

Collect all 45 Fortune Dolls, then boss mode will be available in the options screen!

Hidden Image:

Beat Boss mode & in the end you'll see a special image of Goemon & the gang!

Unlock "I Am Impact" In Sound Test:

After the first Impact Boss battle, the song will be available in Soundtest.

Unlock "Gorgeous My Stage" In Sound Test:

Save the game before the very last Impact battle & you'll recieve the song.