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