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