Here is the full list of all 35 Eternity: The Last Unicorn achievements.
Defeat the Spider Queen
Defeat Úlfrstórr
Defeat Skogul for the first time
Defeat the Old King Wolfric
Defeat the Swamp Tentacle
Defeat Skogul for a second time
Defeat Erick the Corrupted
Defeat Helviti
Defeat Gullveig
Upgrade the Elven Sword to the maximum
Upgrade the Skadian Bow to the maximum
Upgrade the Sword and Shield to the maximum
Upgrade the Two-handed Sword to the maximum
Upgrade a character to the maximum
Upgrade the Eir Medallions to the maximum
Purify all corrupted bodies
Release all bodies corrupted by the swords
Collect 10.000 shards
Collect all the Scrolls of Elros
Complete the Book of Biographies
Beat all the arenas
Deliver Durin's Hammer
Release the fairy
Release Zenogb from the witch's dungeon
Ring the bell in the Gullveig's tower
Get the Skadin Bow
Get the long jump
Finish the game
Talk to the Oracle in the Yggdrasil Garden
Get the light flask in Makala's temple
Find the Lord of the Forest
Beat the arena mode with a character
Collect all the chests
Forger 10 different items
Collect all Trophies