Here is the full list of all 26 BIT.TRIP BEAT achievements.
Block all Beats in all Challenges
Beat the game in one sitting without getting a Game Over
Achieved a multiplier of 50 in Normal difficulty
Chained 500 Beats
long fall
Watched the hidden cutscene
Beat the game on Normal
Beat Growth in Normal difficulty
Get a PERFECT in 1-1 using only a game pad
Beat Descent in Normal difficulty
Chained 200 Beats
Make a bell chime in Descent
Got a PERFECT in sunny 1-1
Block all Beats during a Challenge
Block 10,000 Beats
Beat Transition in Normal difficulty
Register a high score on the leaderboards
Chained 100 Beats
Miss a Beat with an extended Paddle
Escaped Nether Mode
Got a PERFECT score in Transition
Got a PERFECT score in Descent
Got a PERFECT score in Growth
Achieved a multiplier of 100 in Normal difficulty
Got a PERFECT in GLaDOS' level
Experience the joy of a serene suburban afternoon