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