Here is the full list of all 35 Avernum 2: Crystal Souls achievements.
Complete all three game-winning quests in Avernum 2 and never set the difficulty below Hard.
Complete all three game-winning quests in Avernum 2 and never set the difficulty below Torment.
Complete all three game-winning quests in Avernum 2 and never set the difficulty below Normal.
Slay the commander of the invading army.
Make there be one fewer dragon. (Normal difficulty or higher.)
Keep the Empire from flooding Avernum with troops.
Learn 20 mage spells at level 3.
Learn 20 priest spells at level 3.
Win Avernum a powerful ally in its war.
Get a really sweet sword.
Return a Crystal Soul.
Have fifty potions made.
Have ten potions made.
Fill up a spirit prism.
Dig up 40 caches.
Escape the bonds of gravity.
Avenge the lost Avernites of Cotra.
Slay Elderan.
A sharp knife. Find one.
Sanctify 5 altars.
Find each class of Empire pass.
Learn 8 mage spells at level 3.
Learn 8 priest spells at level 3.
Fully prove your worth to Avernum.
Meet the greatest mage in Avernum.
Discover 70 locations of interest.
Learn a priest spell at level 3.
Dig up 10 caches.
Return to Avernum from the depths.
Survive a long river journey.
Discover 20 locations of interest.
Learn a mage spell at level 3.
Meet an envoy from the deepest caves.
Open a secret door.
Escape the caves above Fort Ganrick.