Here is the full list of all 17 Metal Tales: Fury of the Guitar Gods achievements.
Beat level 2: Fall of the Hammer
Beat Cyborg
Beat level 1: Horns & Skulls
Beat Heikegami
Beat challenge room no damage
Beat Hrungnir
Beat Cernunnos
Beat Kresnik
Beat Ottavio
Beat Timo
Beat Kuk
Beat level 3: Nightmare Fest Camp Zone
Beat level 4: Nightmare Fest Main Sta
Beat level 5
Spend 100 coins in the shop
Save 5000 minions
Die 100 times