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