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