????????
      +---------
WLHTG | RWJMZRWW
       -YGHVZ
        =====
        XLJHUR
       -XWQGQL
        ======
          MUWPW
         -WLHTG
          =====
          XRWZMW
         -XZPGPU
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
missing: N