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