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