????????
      +---------
YXJWP | HHRNPLYY
       -YXJWP
        =====
        XYXTUL
       -XURWFJ
        ======
         GNNGHY
        -NPXYGL
         ======
          GQPLLY
         -NPXYGL
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
missing: M