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