Here is the full list of all 8 The Overdreamer achievements.
Check all the places in the hospital.
Check all the places in the house.
Check all the pictures in the house and the basement.
Break all the spider eggs before they hatch.
Break all the boxes and glasses at the Boogeyman's place.
Don't suffer any damage from the roots.
Run through under "Mom's" arm when she tries to hit you.
Find the orange mushroom.