????????
      +---------
TWMXY | TYRTRTUJ
       -TWMXY
        =====
         MFJTT
        -TWMXY
         =====
         WTMJFU
        -WUUJJM
         ======
          JRGHNJ
         -JGGTMF
          ======
          ??????

base: 13
letters: FGHJLMNRTUWXY
difficulty: challenging
missing: L