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