Here is the full list of all 47 Immortals of Aveum achievements.
Completed "Yltheum"
Defeated 100 Enemies
Completed "The Magnus"
Completed "Streetwise"
Completed "The Immortals"
Completed "The Hand of Sandrakk"
Completed "Nocea"
Completed "Exile"
Completed "The Magic Eaters"
Completed "Caldera"
Completed "The Binding Mark"
Completed "Colossal"
Completed "Ruin"
Completed "Occupation"
Completed "Glaivegate"
Completed "The Shrouded Realm"
Completed the game on Apprentice difficulty
Completed the game on Magnus difficulty
Completed the game on Immortal difficulty
Spoke to everyone at the party
Spoke to Silas Mede about every topic
Spoke to Ambassador Damolie about every topic
Spoke to Magister Belming about every topic
Spoke to Hauser about every topic
Spoke to Orphe about every topic
Collected 50 Lore Texts
Fully Upgraded 1 Legendary Sigil
Fully Upgraded 1 Legendary Totem
Fully Upgraded 1 Legendary Bracer
Obtained 3 Legendary Blue Sigils
Obtained 3 Legendary Red Sigils
Obtained 3 Legendary Green Sigils
Obtained 1 Legendary Blue Totem
Obtained 1 Legendary Red Totem
Obtained 1 Legendary Green Totem
Defeated 500 Enemies
Defeated 1300 Enemies
Unlocked all Talents in Blue Magic branch
Unlocked all Talents in Red Magic branch
Unlocked all Talents in Green Magic branch
Completed 10 Shroudfanes
Completed all Shroudfanes
Defeated All of The Six
Opened all Golden Chests in the main story
Found the bird in the Palathon
While looking for Thaddeus, returned from Kalthus to the Palathon
You pet the Veki