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