????????
      +---------
XYNQT | EHHNNUTG
       -EFGNG
        =====
         EXHQU
        -XYNQT
         =====
         XEFHQT
        -XNGHUN
         ======
           TJXFG
          -QEWJF
           =====
           ?????

base: 13
letters: EFGHJMNQTUWXY
difficulty: hard
missing: M