Here is the full list of all 22 Absolver achievements.
Have Cargal kill Kilnor (or the opposite)
Kill 100 Players Character (Any Character)
Open all cairns with one character
Reach Gamemode Level 5
Become an Absolver
Kill Risryn
Kill all marked ones with one character
Join a school
Kill Cargal & Kilnor
Master 1 new Attack
Win 1 PVP Duel
Loot 1 weapon
Kill Kuretz
Push AI off ledge
Kill your opponent with his own weapon in 1v1
Become a disciple of your school
Create a school
Kill all bosses in their last level with one character
Unlock all fighting styles with one character
Master all attacks with one character
Reach Gamemode Level 100