Here is the full list of all 22 Absolver achievements.
Master 1 new Attack
Push AI off ledge
Win 1 PVP Duel
Reach Gamemode Level 5
Loot 1 weapon
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 Kuretz
Kill Cargal & Kilnor
Kill Risryn
Kill all marked ones with one character
Have Cargal kill Kilnor (or the opposite)
Kill 100 Players Character (Any Character)
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