Full sound test
After getting all medals, enter the Squeaks' airship (note that it does not appear in the final world) and give them to Daroach. After he unlocks the last extra, any songs in the sound test that were previously blank (i.e. they never played in the playthrough this is done in and were displayed as question marks) will be available to play in the sound test.
Full sound test - Obtain all medals and give them to Daroach
Fight Galaxia in Kirby Quest
To fight Galaxia, you must select chapter four in the Kirby Quest mini-game. If you do not miss at all, Galaxia will replace Meta Knight on the 39th battle. Note that it will still appear if you get goods or greats, as long as you don't outright miss.