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