Here is the full list of all 14 Opus Mortem achievements.
Maximize Pure Souls
Maximize Evil Souls
Maximize Chrono's Will
Maximize Patience
Maximize Sloth
Maximize Greed
Reach combo x9
Maximize Expertise
Maximize Equilibrium
Collect 100,000 souls
Maximize Resilience
Maximize Temperance
Collect 10,000 souls
Collect 10 souls