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