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