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