Here is the full list of all 16 BIT.TRIP VOID achievements.
Turn all enemy Voids black and collect them during the Ego boss battle before beating the level
Chained 200 Beats
Beat Id in Normal difficulty
Register a high score on the leaderboards
Race against the Id boss for 2 minutes before beating the level
Escaped Nether Mode
Chained 100 Beats
Chained 500 Beats
Watch the hidden cutscene
Beat Ego in Normal difficulty
Beat Super-ego in Normal difficulty
Beat the game in one sitting without getting a Game Over
Collect all black Beats without hitting any white Beats during a Challenge
Collect 10,000 black Beats
Play through an entire stage in Ultra Mode in Normal difficulty
Defeat the Super-ego boss without getting hit by a white Beat