Here is the full list of all 20 Forest of Evil achievements.
Defeat the Hell Hound
Defeat the Lake Serpent
Defeat the Spectral Skull
Defeat the Werewolf
Defeat the Bog Beast
Defeat the Crypt Keeper
Defeat the Man Eater
Defeat the Sorceress
Murder a murder of crows
Press down the button by cutting the cauldron's rope
Hit all of the secret switches in the Maneater Mansion
Hit all of the red eyes in the Catacombs
Die a lot
Hit all the statues with the correct weapon
Defeat all bosses
Finish boss rush mode
Finish hard mode
Discover the grave of the boatman
Unlock all unlockables
Defeat the Night and see the light of day