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