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