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