????????
      +---------
VJXJQ | YPPVMWHL
       -VJXJQ
        =====
        QWLYHW
       - VJXJQ
        ======
         UXMGPH
        -NVGTJL
         ======
          VJLWLL
         -VRVHHY
          ======
          ??????

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