????????
      +---------
JGGMT | YNJRYPJN
       -GMXLJ
        =====
        TTXRVP
       - PWPMZ
        ======
         TQRQMJ
        -TQVRLU
         ======
           VYZRN
          -JGGMT
           =====
           ?????

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