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