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