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