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