Here is the full list of all 44 Valfaris: Mecha Therion achievements.
Destroy every Cerberus Wheel in the Ruins of Anvin.
Defeat Vroll.
Forge the Soul Eater.
Find every weapon.
Defeat the Heart of Jelly.
Defeat Zharn.
Destroy 25 Fuel Canisters in a single playthrough.
Defeat Valkyrie and Kalmah.
Fully upgrade an Auxillary weapon.
Fully upgrade a Melee weapon.
Defeat Garrex.
Find 10 Blood of Valfaris.
Defeat Hern without letting Xyla take a hit. Demigod (Normal) mode or higher required.
Fully upgrade a Destroyer weapon.
Meet Xyla.
Find Eris Ice Axe.
Defeat Gorgoroth.
Defeat Vykham.
Defeat Carnack.
Defeat 20 Champions.
Defeat Tycrid.
Defeat Kykris.
Find Draconis.
Defeat Anvin.
Die for the first time.
Get 666 kills.
Defeat the Jelly Queen.
Find your first Blood of Valfaris.
Upgrade a weapon for the first time.
Find your first module.
Discover a secret area.
Find your first weapon.
Defeat a Champion.
Defeat Herrick without letting Xyla take any damage.
Find every module.
Destroy all sections of a Fenrir Class Destroyer.
Finish a stage without taking any damage. Demigod (Normal) mode or higher required.
Kill all of the Spy Fleas in a single playthrough.
Discover every secret area.
Finish the game in under 2 hours. Demigod (Normal) mode or higher required.
Finish the game with 10 or fewer deaths. Demigod (Normal) mode or higher required.
Finish New Game +.
Defeat Vroll on Great Horned One (Hard) mode.
Defeat Vroll on True Metal mode.