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