Here is the full list of all 21 Void Invaders achievements.
Fire 1,000,000 bullets
Grab a power-up after completing a level
Complete Level Mode
Score over 250,000 in Endless Mode
Reset the game
Die in the tutorial
Fire 500,000 bullets
Stand still for one minute
Complete a level without moving vertically
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 on less than 10% health
Finish the tutorial
Score over 250,000 in Wave Mode
Complete Hardcore Mode