Here is the full list of all 21 Battle for Enlor achievements.
Defeat the greatest of all threaths.
Defeat Mistform, the calamity bringer.
Face the Devourer and live to tell the tale.
Defeat the one that rules the dead.
Defeat someone who was once a great knight.
Achieve a S Rank in the battle against 'Aran, The Black Knight'
Defeat Death.
Defeat the spirit of a pharaoh.
Defeat the one protecting YOU from a terrible fate.
Finish a battle with only one character alive.
Defeat darkness itself.
Achieve a S Rank in the battle against 'Meleera, Queen of the Dead'
Achieve a S Rank in the battle against 'Gnelt, The Devourer'
Achieve a S Rank in the battle against 'Mistform'
Achieve a S Rank in the battle against 'Terr, Scion of Darkness'
Achieve a S Rank in the battle against 'Medragon, Ruler of the Abyss'
Unlock Ceanor, Protector of the Land.
Defeat Seth in its true form.
Achieve a S Rank in the battle against 'a man in a pale white horse'
Achieve a S Rank in the Battle against 'Neheb, Guardian of the Tomb'
Achieve a S Rank in the Battle against Seth.