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