?????????
      +----------
HRYHH | VVGHVJNYY
       -YNRTT
        =====
         LGWTJ
        -JNXXX
         =====
          WURTN
         -NGTJJ
          =====
           WGPVY
          -NGTJJ
           =====
           HMLWWY
          - RQLLL
           ======
           ??????

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