The key to open 6th stage of chapter 6: weird story is an emerald, which you can get by entering 4 numbers of code that guarded by the statue

Doors and Rooms Level 6-6 Walkthrough
you will need pen and paper to copy the number on right stone, then use it in the middle stone to get the 4 password
doors-and-rooms-walkthrough

doors & rooms stage 6-6 solution :
get a book from a bag on floor
get ink beside the bag, it’s fallen
get a hand-shaped stick from a stone statue at the left

use the hand-shaped stick in a hole beside a door and get a fountain pen
combine the fountain pen stained with ink
take the book apart by dismantle and get oilpaper

use the oilpaper on a slate at the right
use the ink-stained fountain pen on the oilpaper and copy the contents of the slate
put the oilpaper on a password translator at the center and close a lid
check the 4 password patterns at the center of the stone statue and find out the 4 number sequence from the password translator :
star – moon – triangle – star

entering the password “6831″ opens the stone statue and reveals a green emerald
use the emerald on the door and unlock the door
open the door and escape