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