Here is the full list of all 25 Watcher Chronicles achievements.
Defeat the Impaler
Defeat the Nephilim Knight
Defeat the Interceptor
Defeat the Crypt Guardian
Defeat the Void Wolf
Defeat the Sadistic Magician
Defeat the Blind Watcher
Defeat the Rogue Knight
Defeat the Jotun Spawn
Defeat the Flesh Golem
Defeat Azrael The Corrupted
Defeat the Ice Golem
Defeat the Warlord
Defeat the Nephilim Construct
Defeat the Masked Watcher
Defeat the Crypt Demons
Defeat the Wraith Lord
Defeat the Bone Dragon
Defeat the Fire Golem
Defeat the Rogue Watcher
Defeat Samyaza
End Eternity
Restore Eternity
Defeat Interceptor II
Defeat Nemesis