?????????
      +----------
VGXJT | LVLVNVVRV
       -VGXJT
        =====
        HJZGVV
       -HXPZMT
        ======
         HLZWNV
        -HZWLYW
         ======
          XTMHVR
         -XJMUWT
          ======
           GNNVHV
          -GLYTXW
           ======
           ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: intermediate
missing: Q