Here is the full list of all 29 Aarklash: Legacy achievements.
You kept Knokka and Frinz together during the whole adventure!
Watch the credits until the end
Complete the game in Rag'narok level of difficulty
Defeat the Golems in Rag'narok level of difficulty with Knokka, Denzil, Frinz and Leck Lorus
Create a male only group
Defeat the first Lord of Pain in Rag'narok level of difficulty without ever pausing the game during the combat
Make an enemy die with a healing spell
Start a new game in Rag'narok level of difficulty; then reach and kill Baron Mornstar without ever pausing the game. Make sure you disable the tutorial and the automatic pause options.
Finish the game
Complete Act III
Find all the chests within the subterranean city
Reach level 20 with one of your units
Find all the chests on the map where the statues show you the way
Solve the mystery of the statues at the beginning of Act 3
Complete Act II
Open the door that leads to the treasure chamber before you meet your Patron Lockshy
Make 10 Epic items
Kill one of your own units with an ally
Reach level 10 with one of your units
Develop a skill to its maximum
Complete Act I
Make 5 Epic items
Be present at the encounter between Knokka and Frinz
Complete the Cave of the Behemoth without ever being hit by a Skeleton Mage projectile
Find all the chests on the map where the Chimera is to be found
Make an Epic item
Defeat the Major Elemental
Reach level 4 with one of your units
Reach level 2 with one of your units