????????
      +---------
FGLFG | QUFYHUHL
       -FGLFG
        =====
         LJGNU
        -YTNYG
         =====
          LFLTH
         -YTNYG
          =====
           NNQNL
          -UFNUX
           =====
           ?????

base: 12
letters: FGHJLMNQTUXY
missing: M
difficulty: medium