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