This guide helps you on getting the secret Deerscent Into Madness achievement in Demonologist.
Unlock Cyclone Street map
The Cyclone Street map is unlocked after reaching level 3. Until then, keep playing.
Enter the house and find the deer
Enter the house, go straight forward into the kitchen and from there into the basement entrance. When looking back, you should see a deer head on the wall.
Say the line
When looking at the deer, say the following line out loud: “I want to join the cult.”
After this a red light should show up next to the head and you should get the Deerscent Into Madness achievement.