????????
      +---------
NTXLY | YXXTWUHZ
       -UGPRJ
        =====
         LLTXU
        -GLHHP
         =====
         NRGTNH
        -XTQRMR
         ======
          XZTXHZ
         -XWNLUP
          ======
          ??????

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