Here is the full list of all 18 Bloodecay achievements.
Defeat Ignatius,the Executioner
Defeat Armored beast
Defeat "The Phoenix"
Defeat The Erosion Shadow
Defeat Man Slayer
Defeat The Crescent Witch
Defeat “Nameless”
Defeat Rotted Angel
Defeat Edward Chester,Hunter of the Lake
Defeat Human Skin Spider
Defeat Liska,the Bloodstained Knight
Defeat Wandering Prince
Defeat Isabel,the King’s Guard
Defeat Viona,the Senior Judge
Defeat Shell of the Erosive deity
Discover the unknown ending
Discover the final ending
Defeat Avalyn Meredith