Here is the full list of all 11 Epic Flail achievements.
UNLOCKED INITIATUS
UNLOCKED CHAINUS
UNLOCKED DISLIKUS
UNLOCKED PLATFORMUS
UNLOCKED MINOTAURUS
UNLOCKED BUTCHERIUS
UNLOCKED ZIUS
UNLOCKED ETECETERUS
UNLOCKED EPIC HELMET
UNLOCKED EPIC SHIELD
UNLOCKED EPIC ARMOR