????????
      +---------
MNFXW | JNJLYWMU
       -QQHMF
        =====
        FUWUNW
       -FFWMYX
        ======
          YJNYM
         -QQHMF
          =====
          HFXXHU
         -UYNRHM
          ======
          ??????

base: 13
letters: FGHJLMNQRUWXY
difficulty: hard
missing: G