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