TRVG
      +---------
NTLWT | XUYPXUGX
       -NTLWT
        =====
        VLQLWU
       -VJWVNR
        ======
         GYHLRG
        -GNQGWV
         ======
          TNJXXX
         -TJGZNG
          ======
           ZHQVM

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: challenging
missing: M