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