Here is the full list of all 20 Unforgotten achievements.
Persuade the villagers to free the man with deer skin.
Persuade the man with deer skin not to fight to the death.
Finish the game as the cult leader.
Get a potion from a chest.
Find an old photograph in the kitchen.
Receive a gift from the mysterious girl.
Seduce a girl in a dark cloak.
Obtain an amulet fighting with Egor.
Find a mysterious altar in the forest and rest near it.
Peek at the old shaman.
Knife Egor.
Finish the game escaping from the weird settlement.
Craft a stone knife while being held captive.
Win a fight with the man with deer skin.
Finish the game becoming a ritual sacrifice.
Solve a puzzle in the mine and obtain Egor's knife.
Quarrel with Egor to get imprisoned.
Complete the prologue to wake up in a strange house.
Break a chest in an attempt to open it.
Start a new day in the weird settlement.