Here is the full list of all 29 Decay of Logos achievements.
Play your role as a pawn in Master Yaal's revenge plot.
Release the trapped youths after defeating Prince Kairos and Mother Reba.
Defeat Prince Pathos.
Defeat Prince Ethos.
Defeat Prince Kairos and Mother Reba.
Lose the battle against King Telos.
Defeat Master Yaal.
Defeat the axe-wielding Ancestral Brute in Laetus Grove, one of the lumberjack twins.
Defeat the vengeful Ancestral Brute in Palus, the last of the lumberjack twins.
Defeat the imprisoned Ancestral War Chief.
Defeat the Slug behemoth.
Defeat one of the Royal Elite Soldiers of the Realm.
Execute Master Yaal.
Open all the chests.
Read all the Ancestral rune stones.
Collect all the memory ripples contained in the Echo Shells.
Free Eitan and exhaust all his dialogue lines.
Release the Masked Boy from the cage and exhaust all his dialogue lines.
Meet Yoran and exhaust all his dialogue lines.
Knock on Nediva's door in the Bosk of Silens and exhaust all her dialogue lines.
Find Nuri in the Hamlet and exhaust all her dialogue lines.
Pick up one of each Mask type worn by the Masked Youths of the Wadi.
Collect all the pieces of King's Guard armor set.
Learn all the Magicae Twines taught by the young Magus.
Unlock all the achievements.
Defeat the Chomper behemoth.
Turn your back on Master Yaal, leaving him to his fate.
Survive the battle against King Telos until the very end.
Defeat all the remaining Ancestral Brutes.