Here is the full list of all 21 Void Invaders achievements.
Score over 250,000 in Wave Mode
Play the game with the volume turned down
Die in the tutorial
Complete a level without moving vertically
Fire 1,000,000 bullets
Score over 250,000 in Endless Mode
Fire 500,000 bullets
Grab a power-up after completing a level
Complete Level Mode
Die 50 times
Stand still for one minute
Destroy 2500 enemy bullets
Kill 2,000 enemies
Pick up 100 powerups
Complete a level on less than 10% health
Kill 1,000 enemies
Complete a level without losing health
Unlock your first skin
Finish the tutorial
Reset the game
Complete Hardcore Mode