Master level difficulty
To unlock as master difficulty, get an A rank in one of the tracks. You will then have a new difficulty level. It is (as far as I can tell) exactly like hard mode but with less warning when the heads will appear.
Track 21-25
Complete tracks 1-20 all the way through on any mode.
Bonus tracks
Play all twenty tracks to unlock a further five tracks to keep you occupied. The bonus tracks are Gotta Get Through This (Daniel Bedingfield), Keep On Moving (Five), Aserjer? (Las Ketchup), Rubberneckin (Elvis Presley), and Addicted To Bass (Puretone).
Score big
To score big, play perfection in the tournament mode against another player. This will hopefully improve your timing.
Home-made games
The following is a list of fun games you can invent to keep the groove going. They are best played with two or more players.
Perfection
The person with the most amount of perfects wins; points are irrelevant.
Battle Of The Gods
Play "Praise you", "Rubberneckin", and "Addicted to Bass" all under the hard difficulty setting. The player with the biggest score out of those three rounds combined wins. Note: This requires the bonus tracks.
Danceathon
Play all twenty five songs in a row on any mode. The player with the biggest score out of all those rounds combined wins. Note: This requires the bonus tracks.
Goldie Oldie (in order of age)
Play "Dance To The Music", "Jungle Boogie", "YMCA", "We Are Family", and "Let's Groove".
Dance Like Hell
Play "Addicted To Bass" in master mode. You will not last long, but the idea is to see how long you last.
Pain In The Neck
Play "Praise You" in master mode.
Drybone
Set up calorie mode and burn at least 10, 15 or 20 calories.