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