Here is the full list of all 20 The Lost Cube achievements.
Collected 15 guitar picks
Killed by an angry viking
Died 100 times
Killed by a laser beam
Collected 5 guitar picks
Died 50 times
Died 20 times
Collected your first guitar pick
Died for the first time
Collected 30 guitar picks
Killed by a green slime
Killed by a bat
Killed by a frog
Fell in a pit of acid
Killed by a cricket
Killed by a flying creeper
Killed by a crawler
Completed the first chapter
Completed the second chapter
Completed the third chapter