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