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